StatementExecutionApiClient - Execute, Get & GetResultChunk should be trim friendly by using source generation

We were looking to disable reflection based JSON serialisation in our application only to hit a stumbling block with the `StatementExecutionApiClient` that we use.

After looking through the code there should be no reason why it cannot be updated to use source generation instead of relying on reflection.

Start at StatementExecutionApiClient and inspect the Execute, Get, and GetResultChunk entry points. Trace how they currently serialize JSON and identify the existing project tests or examples covering these calls. Done means these methods use source-generated serialization and remain compatible with trimming, with relevant behavior still passing.

Written by the indexing model from the issue text.