docs: cleanup clob docs/commands

[ethdew19]

Add clob feature flag to example run commands, and update docs to reflect that it's behind a feature flag now.

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Note

Low Risk
Low risk documentation-only changes that update example run commands and module docs to match feature gating; no runtime logic is modified.

Overview
Updates all CLOB examples’ cargo run commands to include the clob feature (including WS and heartbeats variants) so they match the examples’ required-features.

Adjusts src/clob/mod.rs docs to state the module is behind the clob feature flag and trims the optional-features list accordingly.

^{Written by Cursor Bugbot for commit 1895bb3. This will update automatically on new commits. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.45%. Comparing base (8c98bb8) to head (1895bb3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #295   +/-   ##
=======================================
  Coverage   85.45%   85.45%           
=======================================
  Files          32       32           
  Lines        5121     5121           
=======================================
  Hits         4376     4376           
  Misses        745      745           

Flag	Coverage Δ
rust	85.45% <ø> (ø)

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