Support 64-bit integers in daemon XML-RPC

[sylvesterkaczmarek]

Summary

Fixes #629.

Python's standard XML-RPC marshaller rejects integers outside the signed 32-bit range even though its unmarshaller supports the standard i8 extension.

Register a custom integer marshaller that:

• preserves the normal int tag for signed 32-bit values
• uses i8 for signed 64-bit values
• continues rejecting values outside signed 64-bit range

This allows daemon RPC payloads to carry 64-bit integer values without changing existing 32-bit output.

Testing

Added focused round-trip coverage for:

• signed 32-bit values using int
• positive and negative values outside 32-bit using i8
• signed 64-bit boundaries
• rejection outside the signed 64-bit range

Did you use Generative AI?

Yes. AI was used to assist with tests.

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[fujitatomoya]

the implementation to patch the mashaller looks good to work, but i would take the other path to address the root cause such as JSON-RPC 2.0 over the existing loopback HTTP transport. at least, this needs to be tested.

[fujitatomoya]

i think we need an actual test with xmlrlc client via ros2daemon.

[sylvesterkaczmarek]

Thanks. I added transport-level coverage using ros2daemon's own make_xmlrpc_server() together with DaemonNode, so the test now sends and receives a 64-bit integer through the actual HTTP/XML-RPC client/server path.

I kept this PR scoped to compatibility with the existing XML-RPC transport. Moving the daemon protocol to something like JSON-RPC would be a substantially larger architectural change and can be considered separately.