feat(testing): add SQLx/Rust test framework infrastructure

Add comprehensive Rust/SQLx testing infrastructure to replace pgTAP:

**Core Framework:**
- Create tests/sqlx crate with fluent assertion API
- Add selector constants to eliminate magic string literals
- Implement query assertion builder for ergonomic test writing

**Test Infrastructure:**
- Add SQLx migrations for EQL installation and test helpers
- Add SQL fixtures for test data seeding
- Configure Cargo workspace integration

**Tooling & Scripts:**
- Add mise tasks for test execution and coverage tracking
- Add assertion counting and comparison tools
- Add function call tracking for coverage analysis
- Add test inventory generator
- Add master coverage check script

**Configuration:**
- Update Docker Compose with track_functions enabled
- Add generated migration files to gitignore
- Update mise.toml with Rust test tasks

**Migration:**
- Remove pgTAP testing infrastructure (Dockerfile, tests, scripts)
- Add SQL-to-SQLx migration guide documentation
- Add assertion count and test inventory docs

This infrastructure enables writing Rust tests with SQLx queries instead
of pgTAP, providing better IDE support, type safety, and debugging.

Author: tobyhede

.gitignore

@@ -206,4 +206,7 @@ release/
 __pycache__
 
 # dbdev
-eql--*.sql
+eql--*.sql
+
+# Generated SQLx migration (built from src/, never commit)
+tests/sqlx/migrations/001_install_eql.sql