chore(huey): drop transaction based tracing

[pnagre05]

Description

I removed the transaction-based tracing fallback from the Huey integration - I did this by doing the following:

• Removed all has_span_streaming_enabled branching and enforced the use of sentry_sdk.traces.start_span for both patch_enqueue and patch_execute
• Removed legacy compatibility utilities like the else: fallback blocks and the legacy continue_trace/set_status calls on scope.transaction
• Deleted transaction-based tests (like the has_span_streaming parameterization) and updated the remaining test suite to unconditionally validate span streaming payloads instead of legacy transactions

Issues

• resolves: Remove transaction-based tracing from huey #7095

Reminders

• Please add tests to validate your changes, and lint your code using uv run ruff.
• 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