feat: asof_join_aligned distributed

[colin-ho]

Replaces #7073, which GitHub permanently locked when its base branch (euan/asof-join-aligned) was deleted on #7072's merge. Same branch, rebased onto main.

Implements the shuffle-skipping execution path for join_asof(..., _assume_sorted_and_aligned=True) against #7072's test suite.

• Instead of a separate AsofJoinAlignedNode, AsofJoinNode takes an assume_aligned flag: the aligned path zips input partitions by index (validating partition counts at execution time) and skips sampling + range shuffle entirely. Both paths share the carryover and join-dispatch machinery.
• Fixes a latent carryover bug in the shuffle path along the way: the per-bucket top_n(1) reduction kept only one row per bucket (the lexicographically extreme (by, on) tuple), losing other groups' cross-partition matches. Carryovers are now per-group extreme rows, and each partition's join task receives the extremes of all preceding/following partitions, so matches survive empty and group-sparse partitions. feat: tests for aligned asof join #7072's ≥3-partition tests fail without this and pass with it.
• Re-enables the partition-count-mismatch validation test.

Note: for very high cardinality by keys over many partitions, shipping all per-partition extremes to every join task is O(P²·G) rows worst case; a cumulative per-group merge (O(P·G), but a sequential task chain) is a profile-first follow-up.

🤖 Generated with Claude Code

[github-actions]

Rust Dependency Diff

Head: 42251eb3f672eb4b882b5313a4bdd297bc13de76 vs Base: 525c393b085daddd05adbefada7672b300c096cd.

✅ OK: Within budget.

• New Crates: 0
• Removed Crates: 0

[codecov]

Codecov Report

❌ Patch coverage is 2.94118% with 165 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.92%. Comparing base (f1f4dd2) to head (7583ae4).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ft-distributed/src/pipeline_node/join/asof_join.rs	1.19%	165 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7107      +/-   ##
==========================================
- Coverage   76.29%   75.92%   -0.37%     
==========================================
  Files        1157     1157              
  Lines      164609   164815     +206     
==========================================
- Hits       125586   125138     -448     
- Misses      39023    39677     +654     

Files with missing lines	Coverage Δ
...uted/src/pipeline_node/join/translate_asof_join.rs	97.53% <100.00%> (+0.09%)	⬆️
...ft-distributed/src/pipeline_node/join/asof_join.rs	10.07% <1.19%> (-4.28%)	⬇️

... and 40 files with indirect coverage changes

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