Add a JSON-RPC method on Fendermint for ipc_sendNativeMessage

[dtbuchholz]

Issue type

Feature Request

Have you reproduced the bug with the latest dev version?

No

Version

N/A

Custom code

Yes

OS platform and distribution

N/A

Describe the issue

Developers must use CometBFT APIs to send a raw IPC/FVM message to Fendermint—e.g., in cases where EVM RPCs cannot interact with an actor. This is more challenging in non-Rust languages which don't have access to extensive Rust IPC-related libraries, like Python or JavaScript, but it also enshrines IPC's dependence on CometBFT. Ideally, Fendermint would expose its own RPC with an ipc_sendNativeMessage method, allowing me to submit a message directly to the execution layer instead of CometBFT.

See original context here.

Repro steps

N/A—this is a feature request, not a bug

Relevant log output

No response