fix(parser): handle bytes input in escape_char using to_unicode

[Alm0stSurely]

Problem

escape_char in icalendar.parser.string was annotated to accept str | bytes but used str.replace() operations directly, causing TypeError when bytes input contained characters that needed escaping (comma, semicolon, backslash, newline).

This was flagged by Copilot in the review of #1222.

Analysis

The function signature allowed bytes input, but the implementation used string literals for all replacements. When bytes was passed, Python would raise TypeError: a bytes-like object is required, not str (or similar, depending on the replacement).

The unescape_char function already handles this correctly by branching on isinstance(text, str) vs isinstance(text, bytes). A more consistent approach is to use to_unicode(), which is already available in the codebase and converts bytes to str using the default encoding.

Solution

• Use to_unicode(text) at the start of escape_char to normalize input to str
• Update the return type from str | bytes to str
• Add test_escape_char_bytes verifying all escape patterns work with bytes input

Benchmarks

No performance impact expected — to_unicode is a fast encoding check/conversion that is already used extensively in the parser.

Notes

• This aligns escape_char with the rest of the parser, which uses to_unicode for input normalization.
• The return type change from str | bytes to str is technically a narrowing, but since the function previously crashed on bytes input for most cases, this is a bugfix rather than a breaking change.

Closes #1226

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📚 Documentation preview 📚: https://icalendar--1330.org.readthedocs.build/

[read-the-docs-community]

Documentation build overview

📚 icalendar | 🛠️ Build #32323691 | 📁 Comparing 9cc87b2 against latest (892bc23)

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115 files changed · + 2 added · ± 98 modified · - 15 deleted

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• reference/component-api.html
• reference/design.html

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• 404.html
• genindex.html
• index.html
• py-modindex.html
• _modules/index.html
• contribute/development.html
• contribute/index.html
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• how-to/attendees.html
• how-to/custom-components.html
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• explanation/api-design.html
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• reference/rfc-support.html
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• tutorials/create-event-with-attendees.html
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• reference/api/icalendar.cal.lazy.html
• reference/api/icalendar.parser.ical.calendar.html
• reference/api/icalendar.parser.ical.component.html
• reference/api/icalendar.parser.ical.html
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[stevepiercy]

@Alm0stSurely would you please resolve the merge conflicts, so we can review? Thank you!

[stevepiercy]

Closing due to no response and superseded by #1332