fix serialization issue in streamablehttp mcp tools (#6721)

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The current `StreamableHttpServerParams` has timedelta values that are
not JSON serializable (config.dump_component.model_dump_json()).
This make is unusable in UIs like AGS that expect configs to be
serializable to json,

```python
class StreamableHttpServerParams(BaseModel):
    """Parameters for connecting to an MCP server over Streamable HTTP."""

    type: Literal["StreamableHttpServerParams"] = "StreamableHttpServerParams"

    url: str  # The endpoint URL.
    headers: dict[str, Any] | None = None  # Optional headers to include in requests.
    timeout: timedelta = timedelta(seconds=30)  # HTTP timeout for regular operations.
    sse_read_timeout: timedelta = timedelta(seconds=60 * 5)  # Timeout for SSE read operations.
    terminate_on_close: bool = True
```

This PR uses float for time outs and casts it to timedelta as needed. 

```python
class StreamableHttpServerParams(BaseModel):
    """Parameters for connecting to an MCP server over Streamable HTTP."""

    type: Literal["StreamableHttpServerParams"] = "StreamableHttpServerParams"

    url: str  # The endpoint URL.
    headers: dict[str, Any] | None = None  # Optional headers to include in requests.
    timeout: float = 30.0  # HTTP timeout for regular operations in seconds.
    sse_read_timeout: float = 300.0  # Timeout for SSE read operations in seconds.
    terminate_on_close: bool = True
```

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## Why are these changes needed?

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## Related issue number

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