fix cargo build and cargo clippy warning

[chrislearn]

This PR primarily addresses warnings encountered during cargo build and cargo clippy.

Some basic documentation comments have been added, and some code has been optimized.

opentelemetry_jaeger::new_agent_pipeline appears to be deprecated; it was not modified in this PR but will be fixed in a future PR.

[haixuanTao]

Could we try to avoid empty commit messages?

[haixuanTao]

Some of those change is probably conflict with a bigger PR at #1259

[chrislearn]

Some of those change is probably conflict with a bigger PR at #1259

OK, I set this PR as draft until #1259 merged.

[haixuanTao]

Could we try instead of manually pushing for cargo clippy warning fix use an automated way of fixing clippy warning like https://github.com/MarcoIeni/cargo-assist otherwise we can also try to use something like claude that should detect clippy warning on main and propose a fix without touching at the logic @chrislearn