fix: Selective disabling option for N+1 warnings

[Dibbu-cell]

Description:-
This PR introduces an opt-out mechanism for N+1 detection in the Python SDK so users can selectively mark code paths where N+1-style queries are intentionally acceptable.

Issues:-
resolves: #4887

Reminders:-

Please add tests to validate your changes, and lint your code using tox -e linters.
Add GH Issue ID & Linear ID (if applicable)
PR title should use conventional commit style (feat:, fix:, ref:, meta:)
For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

Hi! This PR is for Hacktoberfest.

Please add the hacktoberfest-accepted label if it cannot be merged soon. Thank you!

[seer-by-sentry]

Potential bug: The allow_n_plus_one() helper only sets tags on the current span, not the parent transaction, when called within a nested span.

• Description: The allow_n_plus_one() function sets tags only on the span returned by get_current_span(). When this function is called within a nested span context, get_current_span() returns the child span, not the transaction. The tags are therefore not propagated to the containing transaction. Since the server-side N+1 detector checks for these tags at the transaction level, the feature will fail to ignore N+1 patterns in the common use case where database operations are wrapped in their own child spans.

• Suggested fix: In allow_n_plus_one(), after setting the tag on the current span, check if span.containing_transaction exists. If it does, set the same tag on the transaction object to ensure the tag is propagated correctly for server-side detection.
  _{severity: 0.7, confidence: 0.95}

_{Did we get this right? 👍 / 👎 to inform future reviews.}