add sync API characterization tests

[harunugurlu]

Summary

• characterize blocking get() wake-up behavior
• characterize timeout and successful get_with_timeout() behavior
• characterize empty and pending try_get() behavior
• verify ordering and no loss across repeated blocking gets
• verify blocked consumers return RuntimeShutdown during detach

Verification

• cargo fmt --all -- --check
• cargo clippy --package aimdb-sync --all-targets -- -D warnings
• cargo test -p aimdb-sync
• make check

Closes #198

[harunugurlu]

@lxsaah Hi, I'm sorry that it took this long for me to do the work. Been extremely busy with my full-time work. I am waiting for your review, thanks!!

[lxsaah]

@lxsaah Hi, I'm sorry that it took this long for me to do the work. Been extremely busy with my full-time work. I am waiting for your review, thanks!!

@harunugurlu, don't worry. Thanks a lot for your contribution! I'll have a look as soon as #208 lands. Meanwhile please ensure the the workflows are running successfully. make fmt should fix it!

[lxsaah]

The rest holds up, the mpsc handshake is the right answer to the issue's "no sleep-and-hope" constraint. It also passes unmodified against pre-#208, which makes it evidence the rewrite preserved the blocking semantics. Happy to approve once the two items are in.

[lxsaah]

lgtm!