fix: map JSON Schema enums to EnumSchema

[dimabullet]

Fixes #38.

getSchemeParameter() resolved a property by matching on type alone, so a standard JSON Schema enum ({"type": "string", "enum": [...]}) became a plain StringSchema and the allowed values never reached the model. The existing 'enum' branch expects {"type": "enum", "options": [...]}, which is not JSON Schema and which no MCP server emits, so it was unreachable.

This resolves the enum keyword before the type based matching:

$options = data_get($property, 'enum');

if (is_array($options) && $options !== [] && $this->isEnumOptions($options)) {
    return new EnumSchema($name, $description, array_values($options));
}

Because the method recurses through $this for items, enums nested inside arrays are covered as well, without extra handling.

isEnumOptions() guards the case Prism cannot type: EnumSchema derives its own type from the options and only handles strings and numbers, so anything else falls through to the existing resolution rather than blowing up.

The old 'enum' branch is left untouched, so nothing that relied on it changes.

Tests

Added an enum_tool fixture to RelayFake and two cases to RelayTest: a string enum and an enum nested in array items. Full suite passes (90 tests), Pint and PHPStan are clean.