[Levan-Demetrashvili]

Fixes #312. Related: python/cpython#158566.

An unfinished escape at the end of a basic string or quoted key reports a position one character past EOF. For a document consisting of a quote followed by a backslash, TOMLDecodeError.pos is 3 even though the document has only two characters.

Advance by the length of the escape slice actually consumed. The incomplete escape now reports EOF (pos == len(doc)) and the correct column, while retaining the existing error message. Complete escapes still advance by two characters.

This is an alternative to #314, which reports the backslash's position. Reporting EOF follows the convention already used for unterminated strings and preserves the existing at end of document message.

The regression test adds 22 subcases covering quoted and dotted keys, table and array-of-table names, values inside arrays and inline tables, multiline strings, CRLF normalization, Unicode, a final unpaired backslash after an escaped backslash, and both loads() and binary load(). It checks the normalized document, position, line, column, and error message. All 22 subcases fail on the unchanged source and pass with the fix.

Validation on Linux:

• Full Tomli unittest suite on CPython 3.12.14, 3.13.5, and a locally built 3.16.0a1+dev debug interpreter; 19 methods on each. The existing Python 3.15+ lazy-import test is skipped on 3.12/3.13.
• Full suite against a mypyc-compiled CPython 3.12 wheel; 19 methods, with the existing pure-Python lazy-import test skipped.
• Coverage: 100% statements and branches across the Tomli source.
• 24,051 differential inputs against the unchanged source, including 733 UTF-8 corpus files and 5,000 Hypothesis examples. Only the expected EOF positions and columns changed; accepted values and rendered error messages were unchanged.
• Black formatting, isort, flake8, mypy, and git diff --check passed for the relevant source/tests. The complete upstream OS/Python CI matrix has not been run locally.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (43a86ad) to head (b6d5c78).

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #326   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            4         4           
  Lines          535       535           
  Branches       100       100           
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  Hits           535       535           

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