Make transformed tool required order deterministic

[Kludex]

Fixes #4565

Snapshot-testing tools/list output was impossible for servers using transformed tools: the JSON changed between test runs. The cause is that TransformedTool built its required array with list(set), so the order depended on Python's per-process hash randomization (PYTHONHASHSEED) — every fresh interpreter could produce a different ordering of the same schema.

This PR makes required follow the schema's property order in both _create_forwarding_transform and _merge_schema_with_precedence, so the wire format is stable across processes (and easier to read). Verified by hashing tools/list JSON under several PYTHONHASHSEED values: previously every seed produced a different result; now they're identical.

base = Tool.from_function(fn)  # fn(alpha, beta, gamma, delta, epsilon)
transformed = Tool.from_tool(base, transform_args={"alpha": ArgTransform(name="a")})

transformed.parameters["required"]
# before: ['delta', 'a', 'epsilon', 'gamma', 'beta']  (varies per process)
# after:  ['a', 'beta', 'gamma', 'delta', 'epsilon']  (always property order)

Label: bugs

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[strawgate]

Lgtm