fix: preserve schema definitions in generated MCP tools

[shalarn1]

The customizer was removing schema definitions ($defs) from MCP tool input schemas, leaving schema references dangling and causing "PointerToNowhere" errors when schema references couldn't resolve for tools with complex schemas (ie nested references).

ex:

prev

  🔧 pointInTimeMetrics: 
    name='pointInTimeMetrics'
    title=None description=None
    inputSchema={
        'type': 'object', 
        'properties': {
            'metrics': {'type': 'array', 'items': {'$ref': '#/$defs/MetricAggregation'}}, // unresolved schema reference -> PointerToNowhere error
            'timeAttribute': {'type': 'string'}
            },
        'required': [ 'metrics']
    }
    outputSchema=None annotations=None meta={'_fastmcp': {'tags': ['cortex-api', 'openapi', 'public-eng-intel-metrics-controller']}}

now

  🔧 pointInTimeMetrics:
    name='pointInTimeMetrics'
    title=None description=None
    inputSchema={
        'type': 'object',
        'properties': {
            'metrics': {'type': 'array', 'items': {'$ref': '#/$defs/MetricAggregation'}},
            'timeAttribute': {'type': 'string'}},
        'required': ['metrics'],
        // preserve $defs schema definitions
        '$defs': {
            'MetricAggregation': {'required': ['aggregation', 'metric'], 'type': 'object', 'properties': {'aggregation': {'enum': ['SUM', 'AVG', 'COUNT', 'RATIO', 'MIN', 'MAX', 'P50', 'P95', 'RANKING'], 'type': 'string'}, 'metric': {'type': 'string'}}}
        }
    }
    outputSchema=None annotations=None meta={'_fastmcp': {'tags': ['cortex-api', 'openapi', 'public-eng-intel-metrics-controller']}}

[shalarn1]

This solved the original missing refs issues but $defs contained more nested $ref references (e.g., $ref -> $defs -> $ref chains) and FastMCP could not resolve these complex reference chains. We need to use a dereferencing script to replace ALL $ref with inline schema definitions, and eliminate the need for $defs entirely. See upstream issue: jlowin/fastmcp#1372