chore: removing dry run for queries without positional params

[sachinpro]

b/553446481

Context

Previously, SQLExecDirect always invoked PrepareQuery(query_str) prior to execution. PrepareQuery performs a dry run API call against BigQuery to retrieve query metadata (schema for the IRD, statement type, and job location).

This PR bypasses the dry run call during SQLExecDirect for simple queries without positional or named parameters, populating the IRD directly from the execution response.

Key Changes:

1. Bypass Dry Run in SQLExecDirect:

   • SQLExecDirect now executes queries directly via ActuallyProcessExecute when no parameter bindings exist

2. Response-Driven Statement & Descriptor Handling:

   • Updated google-cloud-cpp to v3.10.0 which exposes statement_type directly in PostQueryResults from the jobs.query response.
   • Implementation Row Descriptor (IRD) is populated dynamically based on the returned response schema and query statement type (binding for SELECT result sets, unbinding for DDL/DML).

3. Multi-Statement Script Refactoring:

   • Added PopulateScriptChildJobs to handle multi-statement scripts (SCRIPT), properly listing and ordering child jobs and resetting to the first statement's result set.
   • Refactored ExecuteScript to share the child-job enumeration and single-statement handling logic with PopulateScriptChildJobs.

   Verification

   1. GHA checks are passing.
   2. Perf benchmarking results proves that this change doesn't degrade performance.