gh-158500: Reject trailing characters in date.fromisoformat

[rupayon123]

Fixes #158500.

date.fromisoformat() currently accepts basic-format date and ISO-week strings with extra trailing characters because both parsers stop after their expected fields without checking that the input was fully consumed. Require complete input consumption in the C and pure-Python implementations, and cover both forms in the shared regression tests.

Validation:

• Reproduced the bug before the change on CPython 3.11.15's C parser and the main-branch pure-Python parser.
• ./python.exe -m test test_datetime --match '*fromisoformat*' passed (122 tests).
• ./python.exe -m test test_datetime passed (1,166 tests, 33 skipped), exercising both pure-Python and accelerated datetime implementations.
• git diff --cached --check and CPython Tools/patchcheck/patchcheck.py passed.

The debug build completed but this machine lacks OpenSSL and several unrelated optional modules; the datetime tests above passed. AI assistance was used to prepare this contribution; I reviewed the diff and remain responsible for it.

• Issue: date.fromisoformat() silently ignores the last two characters of a 10-character basic-format string #158500

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