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>

zellij_socktop_plugin/target/debug/.fingerprint/arrayvec-52d89aa39fe89d07/lib-arrayvec.json

@@ -0,0 +1 @@
+{"rustc":16696009966390864400,"features":"[]","declared_features":"[\"array-sizes-129-255\", \"array-sizes-33-128\", \"default\", \"serde\", \"std\", \"unstable-const-fn\"]","target":10123127388291370278,"profile":2241668132362809309,"path":10845529551968022874,"deps":[],"local":[{"CheckDepInfo":{"dep_info":"debug/.fingerprint/arrayvec-52d89aa39fe89d07/dep-lib-arrayvec","checksum":false}}],"rustflags":[],"config":8247474407144887393,"compile_kind":0}