Fix test descriptions and remove dead code

[Copilot]

Code quality improvements addressing misleading test descriptions, typos, and dead code.

Dead Code Removal

• Remove unused require 'uri' from extensions.rb (comment questioned its necessity; tests confirm it's not needed)

Test Description Fixes

• on_or_before_spec.rb: "should not be valid" → "should be valid" for datetime before restriction (test calls valid!)
• after_spec.rb: "should be valid for datetime is before" → "should not be valid for datetime before" (test calls invalid!)
• multiparameter_handler_spec.rb: "time column" → "datetime column" (tests birth_datetime)

Typos

• helper_methods_spec.rb: "valiation" → "validation"
• railtie_spec.rb: "intializers" → "initializers"
• multiparameter_handler_spec.rb: "should be nil invalid" → "should be nil for invalid"

Project Config

• Add vendor/ to .gitignore

Original prompt

Assess for bugs or improvements

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