feat(blob): add seekable descriptor streams

[XiaoHongbo-Hope]

Summary

• extend the standalone BlobReader from feat(blob): add standalone BlobDescriptor reader #762 with open_blob
• add lazy, incremental range reads and start/current/end seeking
• share the existing request and in-flight byte limiter across batch and stream reads
• preserve catalog-managed credential refresh when reusing table FileIO

This PR contains Rust core support only. C and Go bindings remain separate follow-up work from draft #761. Batch descriptor grouping and IO merge behavior are unchanged.

Testing

• cargo test -p paimon table::blob_resolver::tests --lib (13 passed)
• cargo test -p paimon test_blob_stream_reuses_refreshing_file_io --lib
• cargo clippy -p paimon --all-targets -- -D warnings
• cargo fmt --all -- --check

[QuakeWang]

LGTM