GH-24157: [C++] Add tests for DayTimeIntervalBuilder

[HyukjinKwon]

Rationale for this change

The DayTimeIntervalBuilder class was marked as untested (ARROW-7938). This PR adds dedicated tests to verify the builder's functionality, similar to how TestHalfFloatBuilder tests HalfFloatBuilder.

What changes are included in this PR?

• Added TestDayTimeIntervalBuilder test class with three test cases:
  • TestAppend: Tests basic append operations including nulls and unsafe append
  • TestBulkAppend: Tests bulk append operations with various signatures
  • TestConstructors: Tests all constructor variations (default, with pool, with explicit type)
• Removed the TODO comment from builder_time.h since the class is now tested

Are these changes tested?

Yes, the tests I mentioned are added.

Are there any user-facing changes?

No, test-only.

• GitHub Issue: [C++] Add tests for DayTimeIntervalBuilder #24157

[github-actions]

⚠️ GitHub issue #24157 has been automatically assigned in GitHub to PR creator.

[HyukjinKwon]

@kou do you mind if I ask to take a quick look please? I thought this is pretty strait forward 🙇 .

[kou]

+1

[HyukjinKwon]

/arrow/cpp/src/arrow/flight/sql/odbc/README.md:29: error: Found unknown command '\to' (warning treated as error, aborting now)

Error: `docker compose --file=/home/runner/work/arrow/arrow/compose.yaml run --rm conda-python-docs` exited with a non-zero exit code 1, see the process log above.

is from #48786 fwiw!