fix: preserve input strictness in from_unixtime

[haohuaijin]

Which issue does this PR close?

Found while reviewing #26111; no separate issue. This fix is independent of that PR.

Rationale for this change

from_unixtime(CAST(seconds AS BIGINT)) could incorrectly eliminate a multi-key sort. Ordered input rows (seconds, id) = (1.1, 1), (1.9, 0) produce the same timestamp, but the IDs must be reordered to 0, 1.

What changes are included in this PR?

Propagate the first argument's strict ordering property instead of unconditionally returning true.

What is the testing strategy for this PR?

Three compact SQL cases in datetime/timestamps.slt check the result ordering with and without a timezone, including NULLs, and verify that direct integer inputs still avoid an extra sort. The two regression cases fail without the fix.

Validated with the targeted SQL test file, all 10 from_unixtime unit tests, formatting, and git diff --check.

Are there any user-facing changes?

Yes. Queries with lossy nested inputs to from_unixtime retain required sorts and return correctly ordered rows.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.88%. Comparing base (1da3cf0) to head (2ffb29a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #26414      +/-   ##
==========================================
- Coverage   82.89%   82.88%   -0.01%     
==========================================
  Files        1153     1153              
  Lines      457487   457487              
  Branches   457487   457487              
==========================================
- Hits       379213   379200      -13     
- Misses      55264    55274      +10     
- Partials    23010    23013       +3     

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[jayzhan211]

Thanks @haohuaijin , LGTM

[haohuaijin]

Thanks for your reviews @jayzhan211 , i checked the merge queue fail, look like merge queue itself have some issue, need you help to enqueue again.