Fix RuboCop offenses detected with rubocop-shopify 3.0.0

## 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.

lib/json_rpc_handler.rb

@@ -16,7 +16,7 @@ module JsonRpcHandler
     PARSE_ERROR = -32700
   end
 
-  DEFAULT_ALLOWED_ID_CHARACTERS = /\A[a-zA-Z0-9_-]+\z/
+  DEFAULT_ALLOWED_ID_CHARACTERS = /\A[a-zA-Z0-9_-]+\z/.freeze
 
   # Sentinel return value from a handler. When a handler returns this,
   # `process_request` emits no JSON-RPC response for the request,

lib/mcp/client/oauth/discovery.rb

@@ -37,7 +37,7 @@ module MCP
         # Matches a single `key=value` pair inside an HTTP auth-scheme challenge.
         # `value` is either a quoted string (which can contain commas and spaces)
         # or a bare token, per RFC 7235.
-        WWW_AUTH_PARAM_PATTERN = /\A([A-Za-z0-9_-]+)\s*=\s*(?:"((?:[^"\\]|\\.)*)"|([^\s,]+))/
+        WWW_AUTH_PARAM_PATTERN = /\A([A-Za-z0-9_-]+)\s*=\s*(?:"((?:[^"\\]|\\.)*)"|([^\s,]+))/.freeze
 
         class << self
           # Parses a `WWW-Authenticate` header and returns the parameters of

lib/mcp/configuration.rb

@@ -5,7 +5,7 @@ module MCP
     LATEST_STABLE_PROTOCOL_VERSION = "2025-11-25"
     SUPPORTED_STABLE_PROTOCOL_VERSIONS = [
       LATEST_STABLE_PROTOCOL_VERSION, "2025-06-18", "2025-03-26", "2024-11-05",
-    ]
+    ].freeze
     DEFAULT_NEGOTIATED_PROTOCOL_VERSION = "2025-03-26"
 
     attr_writer :exception_reporter, :around_request

lib/mcp/icon.rb

@@ -2,7 +2,7 @@
 
 module MCP
   class Icon
-    SUPPORTED_THEMES = ["light", "dark"]
+    SUPPORTED_THEMES = ["light", "dark"].freeze
 
     attr_reader :mime_type, :sizes, :src, :theme
 

lib/mcp/instrumentation.rb

@@ -14,9 +14,7 @@ module MCP
       rescue => e
         already_reported = begin
           !!exception_already_reported&.call(e)
-        # rubocop:disable Lint/RescueException
         rescue Exception
-          # rubocop:enable Lint/RescueException
           # The predicate is expected to be side-effect-free and return a boolean.
           # Any exception raised from it (including non-StandardError such as SystemExit)
           # must not shadow the original exception.

lib/mcp/resource_template.rb

@@ -8,7 +8,7 @@ module MCP
       # Applied after `Regexp.escape`, which turns `{` and `}` into `\{` and `\}`.
       # Variable names are restricted to valid Regexp named-group names,
       # so RFC 6570 operator expressions (e.g. `{?query}`) stay literal and never match.
-      VARIABLE_PATTERN = /\\\{([A-Za-z_]\w*)\\\}/
+      VARIABLE_PATTERN = /\\\{([A-Za-z_]\w*)\\\}/.freeze
 
       attr_reader :uri_template_value
       attr_reader :title_value

lib/mcp/server.rb

@@ -963,9 +963,7 @@ module MCP
     end
 
     def index_resources_by_uri(resources)
-      resources.each_with_object({}) do |resource, hash|
-        hash[resource.uri] = resource
-      end
+      resources.to_h { |resource| [resource.uri, resource] }
     end
 
     def error_tool_response(text)