fix: ignore exact empty files in ordering analysis

[xudong963]

Which issue does this PR close?

• Closes Empty Parquet files invalidate file ordering and statistics-based grouping #24647.

Rationale for this change

A file with exactly zero rows cannot violate a sort order, but schema-only Parquet files normally have neither sorting_columns ordering nor column min/max values. Treating those missing values as evidence against the non-empty files can add an unnecessary SortExec; with statistics-based file-group splitting enabled, it can also fail planning with statistics not found.

The Parquet footer row count is already available during listing, so exact empty files can be ignored without additional I/O. Files with absent or inexact row counts remain conservative.

What changes are included in this PR?

• Ignore files with num_rows == Precision::Exact(0) when deriving a common file ordering.
• Exclude exact empty files from MinMaxStatistics and sort-column NULL checks.
• Preserve the mapping from min/max statistics rows to the original input file indices, so filtering an empty file cannot shift or misidentify later files.
• Support the all-files-empty case with correctly typed zero-length arrays.

Are these changes tested?

Yes.

Are there any user-facing changes?

Yes. Scans over ordered Parquet datasets can retain their output ordering when exact empty files are present, avoiding an unnecessary sort, and statistics-based file-group splitting no longer fails on those files. There are no public API changes.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.06299% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.44%. Comparing base (3ace5a0) to head (aa07f9d).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
datafusion/datasource/src/statistics.rs	93.97%	0 Missing and 5 partials ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main   #24648    +/-   ##
========================================
  Coverage   81.44%   81.44%            
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  Files        1118     1118            
  Lines      399560   399671   +111     
  Branches   399560   399671   +111     
========================================
+ Hits       325424   325526   +102     
- Misses      55137    55142     +5     
- Partials    18999    19003     +4     

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[xudong963]

CC @asolimando in case you have time to review the stats improvement.