Fix code quality issues and resolve PHPStan errors

[ghost]

Summary

• Fixes 2 PHPStan type errors in anonymous classes
• Replaces deprecated LazyProp with OptionalProp (5 instances + import)
• Updates testing patterns to use Laravel testbench conventions
• Fixes parameter documentation in helpers.php

Changes Made

PHPStan Type Fixes

• Fixed return type annotations from `Collection<string, string>` to `array<string, mixed>`
• Updated implementations to return arrays instead of Collections

Deprecated API Replacement

• Replaced LazyProp with OptionalProp following deprecation guidance
• Updated import statement accordingly

Testing Pattern Consistency

• Migrated from `Mockery::mock()` to Laravel testbench `$this->mock()`
• Added proper closure variable binding with `use` clause

Documentation Fix

• Fixed missing `$` in parameter documentation for `inertia_location()`

Verification

• PHPStan: [OK] No errors (was 2 errors)
• Tests: 160 tests, 664 assertions - all passing
• Code Style: Laravel Pint compliance maintained
• No breaking changes: All modifications are internal

Impact

Eliminates static analysis errors and removes deprecated API usage while maintaining full backward
compatibility."

[pascalbaljet]

Thanks for this. The PHPStan issues were already fixed in #774, and I prefer to keep testing LazyProp (as it's still used a lot), so I'll close this PR.