Preserve valueless INI options when decoding

[ac1982]

Describe your changes

Loading [app]\nflag\ncount = 2\n with allow_no_value=True currently raises ValueError: the INI serializer attempts int(None) after configparser accepts the valueless option. Preserve None before trying numeric/boolean conversions, including defaults inherited by sections.

Tests cover valueless section/default options, the constructor and from_ini(), empty strings versus missing values, ordinary typed values, and rejection when allow_no_value is omitted or false.

Related issue

Fixes #617.

All-state searches for allow_no_value found no matching issue or PR. Related INI changes #265 (case handling) and #289 (nested structures) do not address this conversion failure.

Validation

Linux, Python 3.12.15, dependencies from requirements.txt and requirements-test.txt:

• Before the fix: INI module runs 19 tests with two errors from the new regressions.
• After the fix: coverage run --source=benedict -m unittest runs 920 tests, 919 pass and 1 skips; total coverage 98%.
• pre-commit run --all-files passes all configured hooks, including Ruff 0.16.9 and mypy 2.3.1.
• Clean main baseline: 917 tests, 916 pass and the same one skips.
• Other Python versions and operating systems remain for CI. This change covers decoding; INI serialization is unchanged.

Checklist before requesting a review

• I have performed a self-review of my code (Codex review; no human review claimed).
• I have added tests for the proposed changes.
• I have run the tests and there are not errors (one existing skip, noted above).

AI disclosure: OpenAI Codex investigated and reproduced the bug, prepared the code/tests, reviewed the final diff, ran verification, and drafted this description.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.52%. Comparing base (7c7be21) to head (5f6214a).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #618   +/-   ##
=======================================
  Coverage   98.52%   98.52%           
=======================================
  Files          64       64           
  Lines        2437     2439    +2     
=======================================
+ Hits         2401     2403    +2     
  Misses         36       36           

Flag	Coverage Δ
unittests	98.52% <100.00%> (+<0.01%)	⬆️

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