build(ci): add dragonfly-client-util request example to Dockerfiles

[gaius-qi]

Description

This pull request updates the Docker build configuration to include the dragonfly-client-util/examples/request example in the Docker images. This ensures that the example code and its dependencies are available in the build context for all relevant Dockerfiles.

Docker build context updates:

• Added COPY instructions for dragonfly-client-util/examples/request/Cargo.toml and its src directory to the ci/Dockerfile, ensuring the example is included in the production build.
• Added the same COPY instructions to ci/Dockerfile.debug for the debug build.
• Added the same COPY instructions to ci/Dockerfile.dfinit for the dfinit build.

Related Issue

Motivation and Context

Screenshots (if appropriate)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 44.41%. Comparing base (ce1f47f) to head (cad8388).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1780      +/-   ##
==========================================
- Coverage   44.43%   44.41%   -0.03%     
==========================================
  Files          91       91              
  Lines       26054    26054              
==========================================
- Hits        11578    11571       -7     
- Misses      14476    14483       +7     

see 1 file with indirect coverage changes

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