fix: do not treat inf and infinity as numbers when spell checking

[raashish1601]

_check_if_should_check skips anything that float() can parse, and has a special case for "nan" (#125). float() also accepts "inf" and "infinity", so those words were never checked either, even though both are in the English dictionary:

spell = SpellChecker()
"infinity" in spell            # True
spell.known(["infinity"])      # set()
spell.correction("infinty")    # 'infinite', "infinity" is never a candidate

This adds "inf" and "infinity" to the same bypass as "nan". Real numbers like "1e5" are still skipped.

Tests: added test_infinity_correction (fails before the change). pytest tests passes (55 tests), ruff check, ruff format --check and mypy spellchecker are clean.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

View in Codacy

🟢 Metrics 0 complexity · 0 duplication

Metric	Results
Complexity	0
Duplication	0

View in Codacy

_{NEW Get contextual insights on your PRs based on Codacy's metrics, along with PR and Jira context, without leaving GitHub. Enable AI reviewer
TIP This summary will be updated as you push new changes.}