fix: replace invalid escape sequences in astparser.py

[Bindkushal]

Fixes SyntaxWarning on Python 3.12+ where '.' in regular string
literals is treated as invalid escape sequence.

Changed '.' to '\.' in FLOAT_REGEXP_STR and RANGE_REGEXP.

[quozl]

Is this related to the recent issues? Can you please review #83 too? Thanks.

[Bindkushal]

@quozl Yes, this addresses the same issue as #83. , I will test #83 and submit the Revieve there

[Bindkushal]

@quozl I reviewed #83 and the update #85 carefully. While the raw string approach is valid, it also modifies AST handling and introduces an unreachable elif isinstance(node, ast.Constant) check on line 496 — the first ast.Constant branch already handles all cases.

elif isinstance(node, ast.Constant):
return node.value

elif isinstance(node, ast.Constant) and isinstance(node.value, str):
return node.value

original cantorl flow was fine, in his updated #85 . The second elif can never be reached — it checks ast.Constant again but the first one already catches all ast.Constant nodes. Dead code. That's a bug he introduced.