Add ExplicitImports.jl and Aqua.jl quality tests

[ChrisRackauckas]

Summary

• Adds comprehensive quality assurance tests using ExplicitImports.jl and Aqua.jl
• Converts all package imports to explicit imports for better code clarity
• Adds new test file qa_test.jl that runs at the beginning of the test suite

Changes

1. Test dependencies: Added ExplicitImports.jl and Aqua.jl to test extras
2. Quality tests: Created test/qa_test.jl with:
   • Aqua tests for ambiguities, dependencies compatibility, piracies, etc.
   • ExplicitImports tests to ensure no implicit imports and no stale imports
3. Explicit imports: Converted all using PackageX to using PackageX: symbol1, symbol2, ...
   • This makes dependencies clearer and reduces namespace pollution
   • Helps catch unused imports and makes code intent more explicit

Benefits

• ✅ Improved code clarity with explicit imports
• ✅ Better dependency tracking
• ✅ Automated quality checks in CI
• ✅ Reduced namespace pollution
• ✅ Easier to understand what symbols come from which packages

Test plan

• Package precompiles successfully
• Quality assurance tests pass (with expected Aqua compat warnings for stdlib packages)
• Full test suite passes
• CI checks pass

🤖 Generated with Claude Code