Migrate logging infrastructure from Serilog to Microsoft.Extensions.Logging with source-generated methods

[qodo-code-review]

Description

• The codebase currently uses Serilog with static logger instances, which creates tight coupling and prevents dependency injection
• Source-generated logging methods via [LoggerMessage] provide compile-time safety, zero-allocation logging, and better performance
• Need to standardize on Microsoft.Extensions.Logging across the secondary indexing module
• Several experimental attributes and unused parameters need cleanup

Deliverables

• Logging Migration: Replace all Serilog static loggers with ILoggerFactory injection and [LoggerMessage] source-generated methods
• Service Rename: Rename UserIndexReadsideService to UserIndexQueryService for clarity
• Extension Types: Convert extension methods in DuckDbExtensions to C# 12 extension types
• Code Cleanup: Remove [Experimental] attributes, suppress warnings, simplify conditionals, and fix async patterns
• Dependency Updates: Update all test fixtures and load testing code to inject ILoggerFactory dependencies

[linear]

DB-1804