Accept integer TOML truncation limits

[DresdenGman]

Fixes #14675.

Register truncation_limit_lines and truncation_limit_chars as int | str. This accepts native TOML integers while preserving existing string-based configuration formats and -o overrides.

The truncation consumer already converts both values with int(). The regression test now runs the existing threshold cases against both INI and native TOML configuration.

Tests:

• PYTHONPATH=src python -m pytest -q testing/test_assertion.py::TestTruncateExplanation::test_truncation_with_config

[Pierre-Sassoulas]

Dupe of #14692, the first thing an AI should do before doing those automated fixes deemed easy should be to check if something already exists. This is the 6th time an AI MR is opened for this; it's infuriating.