chore: version 1.51.0, path-dep the wasm examples, README notes

- socktop, socktop_agent, socktop_connector -> 1.51.0.
- socktop_wasm_test and zellij_socktop_plugin consume the in-repo
  connector via path deps so wasm-feature API drift is caught at PR time
  instead of after publish. Immediately proved out: the wasm requests
  module needed the new sampled_at_ms field, invisible to native builds.
- zellij plugin gains the standalone [workspace] marker (it could not be
  cargo-checked in-tree at all before). NOTE: its lib.rs has pre-existing
  compile errors unrelated to the connector (static mut STATE conflicts
  with register_plugin!, missing BTreeMap import) — needs its own rework,
  out of scope here.
- README: sampled_at_ms in the example payload.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Cargo.lock

@@ -2412,7 +2412,7 @@ dependencies = [
 
 [[package]]
 name = "socktop"
-version = "1.50.0"
+version = "1.51.0"
 dependencies = [
  "anyhow",
  "assert_cmd",
@@ -2431,7 +2431,7 @@ dependencies = [
 
 [[package]]
 name = "socktop_agent"
-version = "1.50.2"
+version = "1.51.0"
 dependencies = [
  "anyhow",
  "assert_cmd",