fix: check codepoint count not byte length in deserialize_char

[leftygbalogh]

Problem

deserialize_char guards against non-char-length strings with:

ust if s.len() != 1 { return Err(PythonizeError::invalid_length_char()); }

s.len() returns the byte length of the UTF-8 string. Any non-ASCII single-codepoint character (e.g. 'ä' U+00E4) is 1 codepoint but 2 UTF-8 bytes, so the guard fires incorrectly and depythonize::<char> returns Err(InvalidLengthChar) for valid input.

This affects every Unicode codepoint above U+007F — Latin Extended, Greek, Cyrillic, Arabic, CJK, emoji, etc.

Fix

ust if s.chars().count() != 1 {

chars().count() counts Unicode codepoints, which is the semantically correct check for the char type.

Test

A new test est_char_multibyte_codepoint is added in de.rs covering 'ä' (U+00E4, 2 UTF-8 bytes). The existing est_char (ASCII 'a') continues to pass.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.57%. Comparing base (0085a18) to head (7ca25d5).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #107      +/-   ##
==========================================
+ Coverage   84.48%   84.57%   +0.09%     
==========================================
  Files           3        3              
  Lines        1186     1193       +7     
  Branches     1186     1193       +7     
==========================================
+ Hits         1002     1009       +7     
  Misses        118      118              
  Partials       66       66              

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[davidhewitt]

Thanks