fix: handle tree-sitter parse() str/bytes contract on Python 3.14

[Mramaran]

Summary

On Python 3.14, tree-sitter's Parser.parse() rejects bytes arguments with
TypeError: argument 'source': 'bytes' object is not an instance of 'str',
while the version aider pins (tree-sitter==0.25.2) accepts only bytes.

This wraps both parser.parse(bytes(code, "utf-8")) call sites with a
try/except TypeError that falls back to passing the raw string, so aider
works on both contracts without changing the pinned dependency.

Files changed

• aider/repomap.py (line 299)
• aider/linter.py (line 220)

Test plan

• pytest tests/basic/test_repomap.py tests/basic/test_linter.py — 52/52 pass on Python 3.13.5
• Full pytest — 446 passed (1 unrelated Windows symlink-permission failure on local env, not present in CI)
• Pre-commit hooks pass: black, isort, flake8, codespell
• Fallback logic verified by simulating both contract directions
• Original reporters to confirm on Python 3.14

Closes #5174
Closes #5164