Support equality with one in opt-in WindowTopN rule

[osipovartem]

What changes

• Recognize rank_col = 1 and 1 = rank_col in the opt-in WindowTopN rule. Other equalities remain untouched.
• Add physical-plan and result regressions for ROW_NUMBER, RANK (including ties), and DENSE_RANK. Preserve the existing sibling-window safety guard.
• Leave enable_window_topn disabled by default.

Validation

• cargo +stable test --profile ci -p datafusion-sqllogictest --test sqllogictests -- window_topn.slt --test-threads 1
• cargo +stable test --profile ci -p datafusion-physical-optimizer --lib (38 passed)
• cargo +stable clippy --profile ci -p datafusion-physical-optimizer --all-targets -- -D warnings
• cargo +stable fmt --all --check
• Independent read-only review approved correctness, regressions, performance, API compatibility, and tests.

Performance scope

Five local synthetic 100k-row runs (median query elapsed): 100 groups, rule off/on 31/18 ms; 90k groups, rule off/on 120/140 ms. High-cardinality plans can regress, which is why this remains opt-in. These numbers are not a Snowplow benchmark. A pushed-down FilterExec projection can also prevent this rewrite. This PR does not change either behavior.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.77%. Comparing base (06aa131) to head (c60ed5a).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #26160      +/-   ##
==========================================
- Coverage   82.77%   82.77%   -0.01%     
==========================================
  Files        1147     1147              
  Lines      450909   450930      +21     
  Branches   450909   450930      +21     
==========================================
+ Hits       373252   373264      +12     
- Misses      54934    54938       +4     
- Partials    22723    22728       +5     

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