Fix Python comprehension filters after each for clause

[amkdown-max]

Summary

• attach zero or more comp_if clauses to each comp_for
• allow filters to appear between multiple comprehension for clauses
• add regression coverage for list, set, dict, generator, and async comprehensions

Why

Python permits every comprehension for clause to have its own sequence of if filters. Lark's grammar instead placed one optional filter after the entire comp_fors sequence, so valid expressions such as:

[(i, j) for i in range(3) if i > 0 for j in range(5) if j % 2 == 0]

failed when the parser reached the second for.

This change mirrors CPython's for_if_clause structure by keeping each clause's filters with that clause.

Fixes #1525.

Validation

• python3 -m tests TestPythonParser
• python3 -m tests (1311 tests passed, 174 skipped)
• pre-commit run --all-files --show-diff-on-failure
• parsed 51 real Python files from lark/ and tests/
• verified the regression with both LALR/contextual and Earley/basic parsers
• verified the synchronous examples are accepted by both CPython and Lark

[erezsh]

Looks good! Just one nit, I prefer -

comp_for: [ASYNC] "for" exprlist "in" or_test comp_ifs
comp_ifs: comp_if*

It's more organized and easier to process. What do you think?

[amkdown-max]

Agreed — this is clearer and keeps the rule easier to process. Updated in 085eba1. The full test suite (1,311 tests), mypy, and all pre-commit hooks pass. Thanks!

[amkdown-max]

Hi @erezsh, just a gentle follow-up: the workflow runs for the latest commit (085eba1) are still awaiting approval. When convenient, could you approve them so the checks can run? No rush, and thanks again!