Duplicate error messages when using `config.validate_keys = true` in params validation

## Bug Description

When using `config.validate_keys = true` in Hanami params validation, extra/disallowed parameters produce duplicate error messages in the validation errors hash.

## Environment

- **Hanami version:** ~> 2.2
- **hanami-controller version:** ~> 2.2
- **Ruby version:** 3.4.4

## Reproduction Steps

1. Create an action with params validation that has `config.validate_keys = true`
2. Define required parameters
3. Send a request with extra parameters that are not defined in the params block
4. Check the validation errors

## Expected Behavior

Each disallowed key should appear only once in the errors hash:
```ruby
{ errors: { foo: ["is not allowed"] } }
```

## Actual Behavior

Each disallowed key appears multiple times with duplicate error messages:
```ruby
{ errors: { foo: ["is not allowed", "is not allowed"] } }
```

## Code Example

```ruby
module Bookshelf
module Actions
module Home
class Index < Bookshelf::Action
params do
config.validate_keys = true
required(:name).filled(:string)
end

def handle(request, response)
halt 422, { errors: request.params.errors } unless request.params.valid?
response.body = "Welcome to Bookshelf, #{request.params[:name]}!"
end
end
end
end
end
```

## Test Case

```
# Request: GET /?name=Bookshelf&foo=bar
# Expected errors: { foo: ["is not allowed"] }
# Actual errors: { foo: ["is not allowed", "is not allowed"] }
```

Reproduce the duplicate errors using Hanami params validation with config.validate_keys = true and an extra key such as foo. Start by tracing the params validation path; add a regression test for the request example, and consider the issue done when each disallowed key appears once with "is not allowed".

Written by the indexing model from the issue text.