Read JSON fields with ok/err, not some/none

[DerekCorniello]

Json accessors return result<T, string> now, so the wrong kind reports what it found instead of a bare none (muxlang/mux-compiler#404).

The example benefits from the change it was written to track: status is not an int becomes a message saying what the field actually held.

Needs a compiler with that change to run, so hold until the release ships.

[greptile-apps]

Greptile Summary

This PR updates the HTTP server example for JSON accessors that now return result<T, string>.

• Replaces some/none matching with ok/err.
• Preserves accessor diagnostics so wrong-kind errors describe the actual JSON value encountered.

Confidence Score: 5/5

The PR appears safe to merge once the required compiler release is available.

No blocking failure remains; both changed error arms now propagate the accessor-provided diagnostic.

Important Files Changed

Filename	Overview
examples/http_server/main.mux	Updates string and integer JSON field accessors to handle result values and return the detailed accessor error; the previously discarded diagnostic is now preserved.

_{Reviews (2): Last reviewed commit: "Pass the accessor error through instead ..." | Re-trigger Greptile}