feat(slimrpc): add slim.yaml config discovery constructors and a2acli slimrpc support

Add `SlimRpcTransport::from_slim_config(remote)` and
`SlimRpcTransportFactory::from_slim_config()` async constructors that
discover `slim.yaml` walking up from CWD (with env var overrides),
initialize the global SLIM service, connect to the node, and subscribe
the local app in one call.

Update a2acli with a new `slimrpc` feature (off by default) that adds
`--binding slimrpc` and `--slimrpc-target <org/ns/agent>` flags. When
used, the CLI bypasses HTTP agent-card discovery and builds a
`SlimRpcTransport` directly from the slim.yaml config.

Point the workspace `slim_bindings` dep at the local
`agntcy-slim-bindings` path (feat/hierarchical-slim-config-loading
branch) and pin transitive `agntcy-slim-*` packages to the versions in
slim-bindings' own lockfile to avoid version conflicts.

Signed-off-by: Sam Betts <1769706+Tehsmash@users.noreply.github.com>

Author: Tehsmash