[pyupgrade] Fix handling of \N in raw strings (UP032)

[denyszhak]

Summary:

Fixes UP032 autofix incorrectly converting raw strings with \N{...} to f-strings, which changes semantics and causes runtime errors.

Fixes #22060

Test Plan

• Added test case for raw strings with \N{...}
• Regular strings with \N{...} still autofix correctly
• All 119 pyupgrade tests pass

[astral-sh-bot]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[dscorbett]

This PR suppresses the fix when a raw string contains \N{. That is suboptimal because there is no need to suppress the fix. For example, r"\N{angle}AOB = {angle}°".format(angle=180) can safely be fixed to rf"\N{180}AOB = {180}°". Instead, a better solution is to suppress for raw strings the pending_escape logic introduced in #21901.

[denyszhak]

This PR suppresses the fix when a raw string contains \N{. That is suboptimal because there is no need to suppress the fix. For example, r"\N{angle}AOB = {angle}°".format(angle=180) can safely be fixed to rf"\N{180}AOB = {180}°". Instead, a better solution is to suppress for raw strings the pending_escape logic introduced in #21901.

@dscorbett @ntBre does it make sense now?

[ntBre]

Thank you! This makes sense to me overall. I just had a suggestion about the FormatString API.

[denyszhak]

@ntBre sorry I somehow missed your response, PR stayed silent and some time after I just stopped checking and only now noticed

I agree with your comments and than you for pushing those commits!