chore(spark): create ResourceDict type alias for resource specifications

[Neha-Nimsatkar]

What this PR does / why we need it:
This PR introduces a centralized ResourceDict type alias (dict[str, str | int | float]) defined in kubeflow.spark.types.types and updates all Spark SDK module signatures (Driver, Executor, client methods, backend methods, and utility functions) to use it.

This eliminates repeated type definition boilerplate across the module and improves type safety for driver and executor resource specifications, addressing design feedback from PR #752.

Which issue(s) this PR fixes (optional, in Fixes #<issue number>, #<issue number>, ... format, will close the issue(s) when PR gets merged):
N/A (Follow-up refactor to PR #752)

Checklist:

• Docs included if any changes are user facing

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