Core: Pass REST auth manager to S3 signer (#2846)

What does this change do?
- RestCatalog now passes its AuthManager into FileIO so downstream
components can reuse a live token.
- S3V4RestSigner now calls the AuthManager’s auth_header() when no
static token is provided, ensuring the signer gets a fresh bearer token.
- Added a unit test to verify the signer pulls the Authorization header
from an AuthManager.

Why is this needed?
- After the AuthManager refactor, the signer no longer received a token,
causing remote signing to 401 for REST catalog users (e.g.,
Lakekeeper/MinIO). This restores token propagation and refresh.

How was this tested?
- make lint
- make test
- uv run python -m pytest tests/io/test_fsspec.py -k auth_manager -v

Closes #2544

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Co-authored-by: Soham <010Soham@users.noreply.github.com>
Co-authored-by: Fokko Driesprong <fokko@apache.org>
Co-authored-by: Kevin Liu <kevinjqliu@users.noreply.github.com>