Fix: skip boolean column when all values are false for optional arrays

[marcsnid]

Change Summary

Fix AdaptiveBooleanArrayBuilder to skip producing an array when all values are false or null for optional columns. Previously, the builder only skipped on all-null:false values triggered array creation even though false is the boolean default value. This makes boolean columns consistent with how integer (0) and string ("") columns handle defaults.

Changes:

• Added has_true_value and optional fields to AdaptiveBooleanArrayBuilder
• finish() now returns None when optional and !has_true_value
• Updated test_metrics_round_trip to reflect that the is_monotonic column (all false/null) is now correctly omitted

What issue does this PR close?

#1449

How are these changes tested?

• Added 4 new unit tests in boolean.rs:
  • test_adaptive_boolean_builder_all_false — all-false optional → None
  • test_adaptive_boolean_builder_false_and_null — mixed false+null optional → None
  • test_adaptive_boolean_builder_false_then_true — false then true → Some(array) with correct values
  • test_adaptive_boolean_builder_all_false_non_optional — non-optional always produces array
• All existing tests in otap-df-pdata continue to pass (including the updated test_metrics_round_trip).

Are there any user-facing changes?

No. This is an internal encoding optimization. Optional boolean columns that contain only default values (false/null) are no longer included in Arrow record batches, reducing payload size.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.24%. Comparing base (993ba07) to head (78256ef).
⚠️ Report is 3 commits behind head on main.

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Flag	BASE (993ba07)	HEAD (78256ef)
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Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2759       +/-   ##
===========================================
- Coverage   88.06%   82.24%    -5.83%     
===========================================
  Files         644      181      -463     
  Lines      246791    52744   -194047     
===========================================
- Hits       217340    43377   -173963     
+ Misses      28927     8843    -20084     
  Partials      524      524               

Components	Coverage Δ
otap-dataflow	∅ <ø> (∅)
query_abstraction	80.61% <ø> (ø)
query_engine	90.75% <ø> (ø)
otel-arrow-go	52.45% <ø> (ø)
quiver	∅ <ø> (∅)

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