feat: add explicit PyPy and Pyodide support

[yisding]

Summary

Makes PyPy and Pyodide support explicit and CI-verified. The library is pure Python with zero runtime dependencies and ships a universal py3-none-any wheel, so it runs unmodified on both — but getting there surfaced two real PyPy bugs (one a crash, one silent output corruption) that are now fixed and regression-guarded.

Pyodide (CPython compiled to WebAssembly) worked out of the box; verified locally against Pyodide 314.0.0 / Python 3.14.2.

Bugs found & fixed

1. Infinite recursion in LANGUAGE_CODES on PyPy (crash)

_LazyLanguageCodes read its backing store via the bound dict.keys(self) view. On PyPy that view's __len__ re-dispatches to the subclass's overridden __len__, so set(dict.keys(self)) recursed infinitely — len(LANGUAGE_CODES) / set(LANGUAGE_CODES) (e.g. pytest's parametrize(sorted(LANGUAGE_CODES))) crashed the whole suite at collection time with RecursionError. CPython reads the view length from C-level storage, so it never surfaced there.

Fix: snapshot the backing keys with a plain comprehension over the unbound dict.__iter__(self) iterator — length-hints nothing, invokes no overridden method, correct on both runtimes.

2. Possessive quantifiers ignore their minimum on PyPy (silent corruption)

PyPy 3.11 (7.3.x) does not enforce the minimum of a possessive quantifier whose minimum is ≥ 1 (++, {n}+, {n,m}+, {n,}+): it matches zero repetitions instead of failing. Minimal repro:

import re
re.search(r'a++', 'b')   # CPython: None  |  PyPy: <empty match at 0>

This corrupted clean=True output: TableOfContentsRule's \.{4,}+ matched zero dots and deleted ordinary trailing numbers ("Send it to P.O. box 6554" → "… box"), and the HTML rules' \w++ / [^&]++ mangled tags and escaped comparisons in prose ("x < 5 and y > 3").

Fix: replace each min-≥1 possessive with the equivalent atomic group (?>X+) / (?>\.{4,}) — a plain repeat (counted correctly by PyPy) made non-backtracking. Exactly equivalent to the possessive form on CPython, keeps the ReDoS-safety guarantee, correct on PyPy. *+ (minimum 0) is left as-is.

Support / tooling

• CI: new pypy-test job (full suite on PyPy 3.11) and pyodide-test job (build wheel → micropip install into Pyodide → Node smoke test of the public API). Both gate build.
• pyproject: add CPython + PyPy implementation classifiers.
• README: document supported runtimes and browser/micropip usage.
• mypy refuses to run under PyPy, so the lone mypy-subprocess test self-skips there (lint/type-check remain on the CPython jobs).

Verification

• PyPy 3.11.13 (7.3.20), full suite: 1976 passed, 1 skipped, 6 xfailed.
• CPython 3.13, full suite: 1977 passed, 6 xfailed, coverage 94.78% (≥ 93 gate).
• Pyodide 314.0.0 smoke test: English/CJK/clean-TOC segmentation, 26 languages, __version__ all correct.
• ruff check + ruff format --check clean.

New regression tests: tests/regression/test_lazy_language_codes_views.py, tests/regression/test_pypy_possessive_quantifier.py. They assert correct behaviour on every interpreter and fail loudly on PyPy if either bug returns.

Note: upstream PyPy bug

Bug #2 looks like an unreported PyPy re bug (possessive minimum not enforced). I searched the PyPy tracker and found no existing report — details and a ready-to-file write-up are in the PR thread / session for maintainer follow-up.

https://claude.ai/code/session_018tBCqG2oj6A4RSy22o1qjg

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Generated by Claude Code

[codspeed]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 22 untouched benchmarks
🆕 4 new benchmarks

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
🆕	WallTime	test_walltime_segment_medium[pypy]	N/A	273.3 µs	N/A
🆕	WallTime	test_walltime_throughput[pypy]	N/A	2.5 ms	N/A
🆕	WallTime	test_walltime_segment_medium[cpython]	N/A	379.7 µs	N/A
🆕	WallTime	test_walltime_throughput[cpython]	N/A	6.1 ms	N/A

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_{Comparing claude/package-pyodide-compat-yrke5l (890a0bb) with main (04066c6)}