perf(transaction): backport O(M+N) fragment matching in build_manifest onto v9.0.1

[devin-ai-integration]

Summary

Backports upstream lance-format#8210 (commit 14c5f3cc, first released only in v11 betas) onto the stable v9.0.1 tag, so the Exa fork can ship the fix in a 9.0.1+exa.1 pylance wheel — the version silk_node's master locks now pin.

Transaction::build_manifest for Update/Delete matched updated fragments against existing fragments with a per-fragment linear scan (updated_fragments.iter().find(|uf| uf.id == f.id)), i.e. O(M×N). On Orion column-backfill commits touching 4096–8192 fragments against a ~1M-fragment table this dominates commit time (and repeats on every conflict retry). The backport replaces it with:

let removed_ids: HashSet<u64> = removed_fragment_ids.iter().copied().collect();
let mut updated_by_id: HashMap<u64, &Fragment> = HashMap::with_capacity(updated_fragments.len());
for fragment in updated_fragments {
    updated_by_id.entry(fragment.id).or_insert(fragment); // first-wins, same as .find()
}

Semantics are unchanged: same first-match duplicate behavior, same overlay carry-forward and RewriteColumns tombstoning, output ordering still follows the existing-fragments iteration. One conflict hunk from the upstream commit (reusing the maps in original_overlaid_frags) was dropped because v9.0.1 doesn't have that code path; the backported test needed merged_generations instead of upstream's compacted_sstables field.

Also bumps python/Cargo.toml to 9.0.1+exa.1 so the fork wheel is distinguishable from PyPI 9.0.1.

Verified: cargo test -p lance --lib dataset::transaction:: — 60/60 pass (incl. the two new tests from lance-format#8210); cargo fmt clean; built abi3 x86_64 + aarch64 manylinux wheels and smoke-tested a real LanceOperation.Update commit.

Supersedes #10 (same backport onto v7.0.0, made obsolete by the silk_node pylance 9.x bump).

Link to Devin session: https://app.devin.ai/sessions/9589ce7177cd42afbae9db44fc352d5b
Requested by: @ryantqiu

[devin-ai-integration]

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