Describe the bug
When using this lib on a Windows environment, a bug appears when trying to run a local server due to an argument passed to the JSON validation process.

To Reproduce
Steps to reproduce the behavior:

1. Download and install Ruby on Windows
2. Download this source code, open folder in terminal
3. Install dependencies with bundle
4. Try running one of the examples, like:

ruby .\examples\stdio_server.rb

5. Notice an error shows up and the server isn't open.

Could reproduce on two Windows machines. Could not reproduce on a Linux environment.

Expected behavior
After running the STDIO example, the server should be up and running.

Logs
PS C:\Users\rechinfo\Downloads\ruby-sdk-main> ruby .\examples\stdio_server.rb
C:/Users/rechinfo/.local/share/gem/ruby/3.4.0/gems/json-schema-6.0.0/lib/json-schema/schema/reader.rb:125:in 'JSON::Schema::Reader#read_uri': Read of URI at C:/Users/rechinfo/.local/share/gem/ruby/3.4.0/gems/json-schema-6.0.0/resources/draft-04.json refused (JSON::Schema::ReadRefused)
from C:/Users/rechinfo/.local/share/gem/ruby/3.4.0/gems/json-schema-6.0.0/lib/json-schema/schema/reader.rb:93:in 'JSON::Schema::Reader#read'
from C:/Users/rechinfo/.local/share/gem/ruby/3.4.0/gems/json-schema-6.0.0/lib/json-schema/validator.rb:559:in 'JSON::Validator#initialize_schema'
from C:/Users/rechinfo/.local/share/gem/ruby/3.4.0/gems/json-schema-6.0.0/lib/json-schema/validator.rb:60:in 'block in JSON::Validator#initialize'
from C:/Users/rechinfo/.local/share/gem/ruby/3.4.0/gems/json-schema-6.0.0/lib/json-schema/validator.rb:60:in 'Thread::Mutex#synchronize'
from C:/Users/rechinfo/.local/share/gem/ruby/3.4.0/gems/json-schema-6.0.0/lib/json-schema/validator.rb:60:in 'JSON::Validator#initialize'
from C:/Users/rechinfo/.local/share/gem/ruby/3.4.0/gems/json-schema-6.0.0/lib/json-schema/validator.rb:270:in 'Class#new'
from C:/Users/rechinfo/.local/share/gem/ruby/3.4.0/gems/json-schema-6.0.0/lib/json-schema/validator.rb:270:in 'JSON::Validator.validate!'
from C:/Users/rechinfo/.local/share/gem/ruby/3.4.0/gems/json-schema-6.0.0/lib/json-schema/validator.rb:288:in 'JSON::Validator.fully_validate'
from C:/Users/rechinfo/Downloads/ruby-sdk-main/lib/mcp/tool/input_schema.rb:54:in 'MCP::Tool::InputSchema#validate_schema!'
from C:/Users/rechinfo/Downloads/ruby-sdk-main/lib/mcp/tool/input_schema.rb:15:in 'MCP::Tool::InputSchema#initialize'
from C:/Users/rechinfo/Downloads/ruby-sdk-main/lib/mcp/tool.rb:74:in 'Class#new'
from C:/Users/rechinfo/Downloads/ruby-sdk-main/lib/mcp/tool.rb:74:in 'MCP::Tool.input_schema'
from ./examples/stdio_server.rb:10:in 'class:ExampleTool'
from ./examples/stdio_server.rb:8:in '

Additional context
Analysing the error, it seems a dependency is trying to read an URI but the input returned is not one.
For some reason it doesn't understand "C:/Users/.../schema/reader.rb" as an URI on Windows, but needs a "file://" prefix.
I'll make a pull request shortly changing that input for the JSON validator.