SSH module async

[precla]

stratoweave/stratoweave#5

This solution uses libuv's polls to handle incoming data.

Compared to the solution in MR1 , it can handle buffers of smaller size: #define BUF_SIZE 512 can be any value. Since it will append the response until it's EOF. THe MR1 solution had the issue that it would only process once and if something doesn't fit in the predefined buffer, then it would just drop it.

Another change is that this solution uses only actor Client and no more Channel actor.

The Client does everything: setup the connection (ssh or netconf), send a payload and get the response

See comment: #2 (comment)

[precla]

Build.act currently points to a fork: https://github.com/precla/libssh/archive/refs/heads/zig-build.tar.gz

Once actonlang/libssh/pull/3 is merged, it can point to it instead of the fork

[precla]

Changes in latest commit.

Redesign SSH Client to async event-driven API using RTS event loop

Replace the synchronous blocking model (uv_run per operation) with an
async callback-driven architecture that integrates with the Acton RTS
event loop. The Client actor now exposes write()/close() methods and
delivers data via on_receive, on_error, and on_remote_close callbacks
instead of the previous get/set_payload + send_payload pattern.

Key changes:

• Use get_uv_loop() (RTS loop) instead of private per-client uv loops
• Simplify C state machine: AUTH → AUTH_KBDINT → CHANNEL_OPEN → REQUEST_TYPE → READY
• Add keyboard-interactive auth fallback when password auth is denied
• Add buffered async writes with partial-write handling
• Make password and subsystem optional; support shell or subsystem channels
• Remove fallthrough between states so each transition gets its own poll cycle
• Rewrite main actor with a NETCONF state machine example
• Add Build.act with libssh zig dependency

Requires latest actonlang libssh build: actonlang/libssh#3