Build manifest datafile stream lazily

[osipovartem]

Summary

• Create fetch/decode futures only as the bounded manifest stream is polled, avoiding an extra O(manifest-count) allocation and URI clones during scan setup.
• Reject masks whose length differs from the manifest list instead of silently truncating.
• Cover mismatched and all-filtered masks; include an ignored stream-setup microbenchmark.

Validation

• cargo +1.99.0 test -q -p iceberg-rust --lib: 198 passed, 2063 ignored on final commit.
• DataFusion-Iceberg: 18 filter, 2 equality-delete, 3 position-delete tests passed.
• cargo +1.95.0 clippy -p iceberg-rust --lib --tests -- -D warnings passed.
• cargo +1.95.0 fmt --all -- --check and git diff --check passed.
• Manual 100k-manifest stream-setup benchmark: 45.3 ms before, 0.5-6 us after in local debug runs. This measures stream construction only, not manifest I/O or end-to-end query latency.
• Independent read-only review: approved; no blocking findings.