Refactor execution_support to resolve SRP violation in execution database mod

[celsowm]

This PR addresses an SRP violation described in docs/srp-violations.md. The helper module execution_support.rs mixed concerns like session access, context building, and batch execution loop logic. It has been removed and its functions extracted to three separate files:

• session_access.rs (with_session)
• context_builder.rs (build_execution_context)
• batch_runner.rs (execute_batch_core_inner, etc.)
  The main execution.rs file now acts as a facade importing these focused modules.

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PR created automatically by Jules for task 16984110117171531336 started by @celsowm

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