fix(typing): Replace type: ignore comments with proper type fixes

[JoshFerge]

Summary

Stacked on #107710. Fixes the # type: ignore comments that were added during the mypy 1.19.1 upgrade by replacing them with proper type-safe solutions.

Changes by category

attr-defined fixes (relay, organization, user_from_signed_request):

• Created get_relay_from_request() and get_relay_request_data() typed helpers in authentication.py
• Updated all relay endpoint files to use the new helpers instead of request.relay / request.relay_request_data
• Used getattr() for request.organization access (returns Any, satisfies mypy)
• Used existing is_user_signed_request() helper for user_from_signed_request

misc fixes (ORM lookups with possibly-None values):

• Added explicit None checks before ORM .get(id=...) calls where the ID could be None
• Used assert ... is not None for authenticated user IDs and organization IDs
• Extracted request.GET.get("id") into a variable to help mypy narrow the type
• Changed filter(project=project) to filter(project_id=project.id) for HybridCloudForeignKey

arg-type fix (base_query_set.py):

• Added isinstance(col, str) check before dict lookup, properly narrowing str | Combinable

unreachable fix (delayed_processing.py):

• Changed instance_data.get("event_id") to instance_data["event_id"] since event_id is a required key in the EventData TypedDict — the None check was correctly flagged as unreachable

Other fixes:

• Removed invalid select_related() on a ManyToManyField (uptime subscriptions)
• Used cast() for Django _meta.get_field() return type in test fixture
• Kept # type: ignore[no-redef] for annotation shadowing model field (genuine mypy limitation)

Remaining type: ignore

One # type: ignore[no-redef] remains in workflow_group_history_serializer.py — this is a known mypy limitation where .annotate(detector_id=...) shadows an existing model field name.

Test plan

• mypy passes on all 21 changed files with 0 errors
• All pre-commit hooks pass
• CI passes