Align ToolMapper with Neuron's mapper contract

Problem/Motivation

Drupal\ai_neuron\Providers\ToolMapper::map() rebuilds each tool's schema one property at a time from ToolInterface::getProperties():

foreach ($tool->getProperties() as $property) {
  $function->setProperty($this->property($property));
}

Neuron's provider contract (src/Providers/AGENTS.md) says a tool mapper "consumes ToolInterface::getInputSchema() rather than rebuilding the schema from properties", and Neuron's own Providers\OpenAI\ToolMapper sends getInputSchema() as parameters and merges getParameters() on top.

Two consequences:

1. A tool that overrides getInputSchema() loses everything the property list does not carry. FrontendTool, which Neuron's AG-UI input translator builds from a client-supplied schema, is the shipped example. For a schema with email {format, maxLength}, count {minimum, maximum} and opts {additionalProperties: false}, getInputSchema() keeps all of these, while the module sends {"email": {"type": "string", "description": "Address"}, "count": {"type": "integer"}, "opts": {..., "required": []}}.
2. Tool::setParameters() (hand-written schema fragments, cache_control and other raw provider keys) is ignored for every tool.

The model therefore gets a looser contract than the tool declares, and validation that the tool author relied on does not happen.

Steps to reproduce

1. Build a FrontendTool with an input schema carrying format, maxLength, minimum or additionalProperties.
2. Run it through ToolMapper::map() and render the resulting ToolsFunctionInput.
3. Compare with $tool->getInputSchema(): the constraints are gone.

Proposed resolution

Map from getInputSchema(): take properties and required from the schema instead of iterating getProperties(), then merge getParameters() into the function definition the way Neuron's OpenAI mapper does. NeuronPropertyInput can stay as the vehicle for passing each property's schema through to drupal/ai unchanged.