#9626 fix: Expand environment variables in mapping configuration Pull request opened by edgarrmondragon ## Description SSIA. ## Related Issues • Closes #7151 • MeltanoLabs/meltano-map-transform#421 ## Summary by Sourcery Fix mapping configuration handling by reordering merge to apply processed values and migrating file writes to async for consistency Bug Fixes: • Process environment variables in mapping configuration Enhancements: • Switch to asynchronous file operations when writing the mapping config ## Summary by Sourcery Fix Singer mapper to process environment variables in mapping configuration and switch to asynchronous file writes Bug Fixes: • Process environment variables in mapping configuration when merging plugin and mapping settings Enhancements: • Use asynchronous file operations for writing the mapping configuration file Tests: • Add test for environment variable expansion in mapping configuration meltano/meltano