Add assert_requirements bindings for pinned-base commit assertions

[gbrgr]

Summary

Wraps RelationalAI/iceberg-rust#83's OverwriteAction::assert_requirements for Julia:

• assert_requirements(action::OverwriteAction, requirements) lets a caller supply arbitrary TableRequirements (as typed subtypes: AssertTableUuid, AssertRefSnapshotId, etc.) alongside the ones an action derives automatically. A supplied requirement of an auto-derived kind replaces the derived one; any other kind is added; repeated calls accumulate.

Why

Transaction::commit's do_commit always refreshes the table from the catalog and silently rebases onto whatever is current before computing its auto-derived RefSnapshotIdMatch requirement, on every attempt, not just retries. That means a retried (or racing) commit would otherwise keep asserting whatever is current rather than the base it actually started from, and a genuine conflict could never surface. assert_requirements lets a caller pin that assertion to an externally-resolved base snapshot instead, so the catalog itself enforces it.

Bumps iceberg_rust_ffi's iceberg-rust git rev to RelationalAI/iceberg-rust#83's branch head to pick up the new API; move this to a main rev once that PR merges.

Test plan

• assert_requirements_tests.jl -- covers override/accumulate/reject semantics against a real in-memory catalog, including two tests that provoke a genuine CatalogCommitConflicts by pinning a stale/wrong requirement and asserting the catalog itself rejects the commit
• overwrite_tests.jl -- unaffected, still green
• cargo build/cargo fmt --check/cargo clippy on iceberg_rust_ffi -- clean

🤖 Generated with Claude Code

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

❌ Patch coverage is 64.00000% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.72%. Comparing base (208160a) to head (03e3418).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/transaction.jl	64.00%	9 Missing ⚠️
❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #116      +/-   ##
==========================================
- Coverage   86.17%   85.72%   -0.46%     
==========================================
  Files           9        9              
  Lines        1013     1058      +45     
==========================================
+ Hits          873      907      +34     
- Misses        140      151      +11     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.