Remove artificial defaults from text nodes

[tefra]

📒 Description

The generator used to give every str/bytes text field an artificial default="". That produced odd models such as a pattern restriction whose default doesn't match the pattern:

value: str = field(
    default="",
    metadata={
        "pattern": r"0x[0-9a-z]*",
    }
)

Text fields are now generated without a default, and the parsers bind the empty value instead. This replaces #1210, which made the same change in a single commit and had side effects in the parsers.

Breaking change: generated simple-content classes now need value passed in, e.g. Comment() becomes Comment(value="").

🔗 What I've Done

• ParserUtils.accepts_empty_text: missing text binds as ""/b"" only when the text field is required, has no default and is str/bytes. Every other field keeps its default or stays unset, as before.
• ElementNode.bind_text and DictDecoder.bind_dataclass use that rule. The dict decoder writes to its params and leaves the input dict untouched.
• SanitizeAttributesDefaultValue no longer sets default="" on text nodes. The fixtures were regenerated.
• Removed the unused default and tokens_factory params from ParserUtils.parse_var.

💬 Comments

Side effects of #1210 that this version avoids:

• an empty element with an int/date/enum text field no longer gets a ConverterWarning and a raw "";
• callable (e.g. enum) defaults are kept;
• fixed init=False text is not validated against "";
• the element tail still reaches a wildcard field;
• a null text value in the dict decoder still falls back to the field default.

Regression suites, run locally with dataclasses output:

• samples: all suites pass, and the XML comparisons and schema validations are unchanged.
• W3C: build 14687 passed, xsd 14600 passed. The skip list is identical to main (87).
• The only output changes are the removed default=""/default=b"" lines, and the pycode dumps now writing value='' explicitly.

🛫 Checklist

• Updated docs
• Added unit-tests
• Sample tests pass
• W3C tests pass

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.97%. Comparing base (cf7afe8) to head (7f0a2e5).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1240   +/-   ##
=======================================
  Coverage   99.97%   99.97%           
=======================================
  Files         117      117           
  Lines        9414     9421    +7     
  Branches     1447     1448    +1     
=======================================
+ Hits         9412     9419    +7     
  Misses          1        1           
  Partials        1        1           

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