Ractor incompatibility: contracts, schemas, types, and results cannot be used from non-main Ractors on Ruby 4.0

`dry-validation` (1.11.1) and its underlying dependencies (`dry-schema`, `dry-types`, `dry-initializer`) cannot be used inside [Ractors](https://docs.ruby-lang.org/en/master/Ractor.html) on Ruby 4.0. No operation works — instantiating contracts, calling them, defining schemas, looking up types, or even passing a validation result into a Ractor.

### Environment

- **Ruby version:** 4.0.3 (2026-04-21)
- **dry-validation:** 1.11.1
- **dry-schema:** 1.16.0
- **dry-types:** 1.9.1
- **dry-initializer:** 3.2.0
- **OS:** Linux x86_64

## Reproduction

Save as `dry_validation_ractor_poc.rb` and run with `ruby dry_validation_ractor_poc.rb`:

```ruby
#!/usr/bin/env ruby
# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
source "https://rubygems.org"
gem "dry-validation", "~> 1.10"
end

require "dry-validation"

version = Gem.loaded_specs["dry-validation"]&.version
puts "Ruby #{RUBY_VERSION}, dry-validation #{version}"
puts "-" * 50

class UserContract < Dry::Validation::Contract
params do
required(:name).filled(:string)
required(:age).filled(:integer, gt?: 0)
end
rule(:name) { key.failure("too short") if value.length < 2 }
end

contract = UserContract.new

tests = {
"Contract.new in Ractor" => -> { Ractor.new { UserContract.new }.value },
"contract.call in Ractor" => -> { Ractor.new(contract) { |c| c.call(name: "Alice", age: 30) }.value },
"Define contract in Ractor" => -> {
Ractor.new {
Class.new(Dry::Validation::Contract) { params { required(:x).filled(:string) } }.new.call(x: "hi")
}.value
},
"Dry::Types[] in Ractor" => -> { Ractor.new { Dry::Types["strict.string"] }.value },
"Dry::Schema.Params in Ractor"=> -> { Ractor.new { Dry::Schema.Params { required(:a).filled(:string) } }.value },
"Pass result across Ractor" => -> { Ractor.new(contract.call(name: "Alice", age: 30)) { |r| r.success? }.value },
}

tests.each do |name, test|
print "#{name}: "
begin
test.call
puts "OK"
rescue Ractor::RemoteError => e
puts "FAILED — #{e.cause.class}: #{e.cause.message}"
rescue => e
puts "FAILED — #{e.class}: #{e.message}"
end
end
```

### Actual output

```
Ruby 4.0.3, dry-validation 1.11.1
--------------------------------------------------
Contract.new in Ractor: FAILED — RuntimeError: defined with an un-shareable Proc in a different Ractor
contract.call in Ractor: FAILED — TypeError: allocator undefined for Proc
Define contract in Ractor: FAILED — Ractor::IsolationError: can not get unshareable values from instance variables of classes/modules from non-main Ractors (@dry_initializer from Dry::Validation::Contract)
Dry::Types[] in Ractor: FAILED — Ractor::IsolationError: can not get unshareable values from instance variables of classes/modules from non-main Ractors (@type_map from Dry::Types)
Dry::Schema.Params in Ractor: FAILED — RuntimeError: defined with an un-shareable Proc in a different Ractor
Pass result across Ractor: FAILED — TypeError: allocator undefined for Proc
```

### Expected behavior

At minimum, pre-built contracts should be callable from non-main Ractors, and results should be transferable across Ractor boundaries. Ideally, defining new contracts and looking up types should also work.