Delegate DirFileSystem delete and write_text

[ShipItAndPray]

Summary

• delegate DirFileSystem.delete() to the wrapped filesystem instead of inheriting the base alias path
• delegate DirFileSystem.write_text() so wrapper filesystems can enforce their own write behavior
• add focused regression tests for both methods

Closes #1997.

Validation

• E1 baseline repro exists: yes
  • The issue's reproduction on baseline allowed both fs.write_text('bar', 'lorem ipsum') and fs.delete('bar') to succeed instead of raising from the wrapped filesystem.
• E2 new regression tests fail on baseline: yes
  • In a temporary HEAD worktree with only the new tests applied:
  • .venv/bin/python -m pytest fsspec/implementations/tests/test_dirfs.py -k 'delete or write_text' -q
  • Result: 4 failed, 134 deselected
• E3 regression tests pass after fix: yes
  • .venv/bin/python -m pytest fsspec/implementations/tests/test_dirfs.py -q
  • Result: 138 passed
• E4 direct issue repro matches expected behavior after fix: yes
  • The issue script now raises NotImplementedError for both write_text and delete, proving delegation reaches the wrapped filesystem.
• E5 diff stays localized: yes
  • Changes are limited to fsspec/implementations/dirfs.py and fsspec/implementations/tests/test_dirfs.py.