Tool outputSchema is generated in validation mode, so serialization aliases and computed fields don't match structuredContent

[jayzuccarelli]

On v2 (2118f14), a tool returning a model with a serialization_alias or a @computed_field advertises an outputSchema that its own structuredContent violates:

from pydantic import BaseModel, Field, computed_field
from mcp.server.mcpserver.utilities.func_metadata import func_metadata

class Out(BaseModel):
    user_id: int = Field(serialization_alias="userId")

    @computed_field
    @property
    def doubled(self) -> int:
        return self.user_id * 2

def tool() -> Out:
    return Out(user_id=3)

m = func_metadata(tool)
print(sorted(m.output_schema["properties"]))                        # ['user_id']
print(sorted(m.convert_result(Out(user_id=3)).structured_content))  # ['doubled', 'userId']

Clients that validate structuredContent against outputSchema (as the spec says they should) reject these results. camelCase serialization aliases are common for JS-facing tools, so this hits anyone using them.

I had a fix for this in #3118 (closed in the v2 cleanup) and can port it to v2 with a regression test if you'd like to assign this to me.