D300: prevent autofix when both triples are in body

[T-256]

Summary

Addresses #8402 (comment)

Test Plan

Added associated test

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[T-256]

Sorry for disabling auto-merge, but I think this should have autofix:

def contains_triples(t):
    '''(\'''|\""")'''

Into

def contains_triples(t):
    """(\'''|\""")"""

[charliermarsh]

I think this is fine to merge as-is because we already get that "wrong" today for the simpler case, I think:

def contains_triples(t):
    '''(\""")'''

Getting it right requires that we parse the entire docstring to track escapes.

[T-256]

Getting it right requires that we parse the entire docstring to track escapes

Correct, I was looking for escape-processed of docstring content to implement it, but didn't find a proper way.
BTW I added a todo example, I also think it's safe to merge for now.

[charliermarsh]

@T-256 - We have some stuff like that in crates/ruff_linter/src/rules/flake8_quotes/rules/avoidable_escaped_quote.rs.