[#2771] feat(spark): Support Spark 4.2 (#2772)

### What changes were proposed in this pull request?

Add a mutually-exclusive `spark4.2` Maven profile that builds the existing `client-spark/spark4` module against **Apache Spark 4.2.0**, mirroring the `spark4.1` profile added in #2751.

- **Root `pom.xml`**: new `spark4.2` profile — a structural clone of `spark4.1`, differing only in `spark.version=4.2.0`, `scala.version=2.13.18`, `netty.version=4.2.13.Final`, `jackson.version=2.21.2`, and the lz4 coordinate (`lz4.groupId` + `lz4.version`, see below).
- **`client-spark/spark4/pom.xml`**: `spark4.2` profile reuses the `src/main/java-spark4_1` compat source root (the 4.1 `Spark4Compat` shim).
- **`client-spark/extension/pom.xml`**: `spark4.2` profile reuses the `scala-jakarta` servlet source root.
- **`client-spark/extension` — `ShufflePage.scala`**: the Uniffle UI tab's collapsible sections use `onClick="collapseTable(...)"`, relying on a global `collapseTable()` that Spark 3.x/4.0/4.1 ship in `webui.js`. Spark 4.2 removed that function (its own pages moved to Bootstrap 5 `data-bs-toggle` collapse), so under `-Pspark4.2` the sections could not be expanded. Inline a fallback that defines a compatible `collapseTable` only when the host Spark didn't provide one — 3.x/4.0/4.1 keep Spark's implementation, 4.2 gets a working equivalent, reusing the `.collapsed` / `arrow-open|closed` CSS every Spark line still ships.
- **lz4**: introduce `${lz4.groupId}` (`org.lz4` by default, `at.yawk.lz4` under `spark4.2`) and `${lz4.version}` (`1.8.1` by default, `1.11.0` under `spark4.2`); the two integration-test modules declare `${lz4.groupId}:lz4-java`, and the `at.yawk.lz4` root-`dependencyManagement` entry is pinned to `${lz4.version}`. The default build and every non-`spark4.2` profile stay on `org.lz4:1.8.1` — the bump is scoped to `spark4.2` only.
- **CI**: `parallel.yml` gains a `spark4.2 / java 17` matrix entry; `sequential.yml` gains a `-Pspark4.2` step gated on `java-version == 17`.

No new Maven module. `client-spark/spark4-shaded` needs no relocation change (its bouncycastle/jctools relocations are already global); a comment was added there noting its lz4 exclusion must stay `org.lz4` — Maven matches exclusions on the as-declared coordinate, so parameterizing it would leak `at.yawk.lz4` into the shaded jar under `-Pspark4.2`.

### Why are the changes needed?

Fix: #2771

Users should be able to build and run Uniffle's Spark client against Spark 4.2.0 with full parity to the existing 4.1 support.

The three cross-major APIs called from `client-spark/spark4` are **byte-identical** between 4.1.1 and 4.2.0 (verified with `javap`), so no shim change is required:

| API | 4.1.1 | 4.2.0 |
|---|---|---|
| `MapStatus.apply(BlockManagerId, long[], long, long)` | 4-arg | identical |
| `ExternalSorter(…, RowBasedChecksum[])` ctor | 6-arg | identical |
| `WebUIPage.render(jakarta…HttpServletRequest)` | jakarta | identical |

Dependency notes:
- **jackson → 2.21.2 (required):** Spark 4.2.0 ships `jackson-module-scala_2.13` 2.21.2, which validates the classpath `jackson-databind` on registration and throws in `RDDOperationScope`'s static initializer if it is outside `[2.21.0, 2.22.0)`. Same class of failure the 4.1 work hit.
- **netty → 4.2.13.Final:** matches what Spark 4.2.0 was compiled/tested against (still Netty 4.2, same major as 4.1's 4.2.7, so #2751's `NioIoHandler`/refCnt handling still applies — no code change).
- **lz4 → at.yawk.lz4:1.11.0, scoped to spark4.2 (required):** Spark 4.2.0 bumped lz4 to 1.11.0 and calls `LZ4BlockInputStream.newBuilder()` (added in the 1.11 line); without it the integration tests fail at runtime with `NoSuchMethodError`. Because `org.lz4:1.8.1` is a relocation stub that Maven rewrites to `at.yawk.lz4:1.8.1`, a globally-managed `at.yawk.lz4:1.11.0` would silently bump lz4 across the whole reactor (server/client/coordinator/…), which is out of this PR's scope and would override the `org.lz4:1.8.1` pin from #2693 (CVE-2025-12183). The `${lz4.groupId}`/`${lz4.version}` properties confine the bump to the `spark4.2` profile; every other build stays on 1.8.1.
- hadoop / jetty / log4j / slf4j / commons-lang3 deltas are deferred; the profile keeps the 4.1 values.

### Does this PR introduce _any_ user-facing change?

No behavioral change to existing profiles. Adds a new opt-in `-Pspark4.2` build profile, and fixes the Uniffle Spark UI tab so its collapsible sections expand under Spark 4.2. Existing `-Pspark4` (4.0.2) and `-Pspark4.1` (4.1.1) are unchanged.

### How was this patch tested?

Verified locally on JDK 17 (Zulu 17.0.18):

1. `mvn clean install -Pspark4.2 -DskipTests` — compiles + shades against 4.2.0 (spark-core/sql/catalyst 4.2.0, scala 2.13.18, netty 4.2.13.Final, jackson 2.21.2, lz4 `at.yawk.lz4:1.11.0` resolved).
2. `mvn clean install -Pspark4.1 -DskipTests` + integration tests — 4.1.1 build and `AQERepartitionTest` / `MapSideCombineTest` still green (lz4 stays `org.lz4:1.8.1`); confirms no regression. Also confirmed the default build (no profile) and other spark profiles keep lz4 at 1.8.1.
3. `AQERepartitionTest`, `MapSideCombineTest` pass under `-Pspark4.2`.
4. `TransportFrameDecoderTest` (2 tests) passes on Netty 4.2.13 under `-Pspark4.2`.
5. `RepartitionWithLocalFileRssTest` (NOOP/ZSTD/**LZ4** codecs) passes under `-Pspark4.2` — exercises the lz4 runtime path.
6. `dev/scripts/checkshade.sh` on the spark4.2 shaded jar — "check success", 0 unshaded classes; bouncycastle/jctools relocated, no `net.jpountz` (lz4) leak.
7. **End-to-end on a real Spark 4.2.0 distribution** against a local Uniffle cluster (coordinator + shuffle server): a shuffle job runs through `RssShuffleManager`, and the Uniffle Spark UI tab renders and its collapsible sections (Build Info / Shuffle Server / Assignment / …) expand with no page JS errors.

CI runs the build + unit + integration tests via the new `spark4.2` matrix entry / `-Pspark4.2` step.