Fix RuboCop offenses detected with rubocop-shopify 3.0.0

[koic]

Motivation and Context

This repository does not track Gemfile.lock, so bundle install resolves to the latest RuboCop gems. Upgrading rubocop-shopify from 2.x to 3.0.0 surfaces 8 new offenses because the shared config no longer disables Style/MutableConstant, newly disables Lint/RescueException and Naming/AccessorMethodName, and drops AllowedPatterns for Naming/MethodName. Upgrading rubocop itself to 1.88 surfaces one more offense from the new Style/ReduceToHash cop.

This change fixes them as follows:

• Freeze mutable constants. Regexp constants are also flagged because TargetRubyVersion is 2.7, where Regexp literals are not frozen.
• Remove inline disable directives that became redundant.
• Restore AllowedPatterns: ['\Atest_'] for Naming/MethodName so def test_ style test names can reference class names such as NoMethodError.
• Swap out the frozen SUPPORTED_STABLE_PROTOCOL_VERSIONS constant in the protocol version fallback test since Mocha cannot stub methods on frozen objects.
• Use to_h instead of each_with_object in Server#index_resources_by_uri.

Ref: https://rubygems.org/gems/rubocop-shopify/versions/3.0.0

How Has This Been Tested?

bundle exec rake passes: 1402 runs, 0 failures, 0 errors, and RuboCop reports no offenses. The conformance suite also passes against its baseline.

Breaking Changes

None. Freezing these constants only affects code that mutates them in place, which has never been supported.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

[koic]

I'll merge this now so upcoming CI runs can pass.