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>

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+/home/jasonw/Documents/GitHub/socktop/zellij_socktop_plugin/target/debug/build/generic-array-76a074935a60a0eb/build_script_build-76a074935a60a0eb: /home/jasonw/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/generic-array-0.14.9/build.rs
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