switch_map followed by box_it fails to satisfy CoreObservable - #280

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.58%. Comparing base (a469003) to head (534c825).

@@            Coverage Diff             @@
##           master     #280      +/-   ##
==========================================
+ Coverage   82.42%   82.58%   +0.16%     
==========================================
  Files          84       84              
  Lines       11756    11929     +173     
==========================================
+ Hits         9690     9852     +162     
- Misses       2066     2077      +11     

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Thanks for the focused reproduction.

The root cause is that SwitchMapOuterObserver did not carry the inner observable type in its own type identity. InnerObs only appeared in the Observer impl predicates, so when switch_map(...).box_it() went through the boxed CoreObservable path, the compiler could not preserve the relation between the downstream observer and InnerObs::Item<'a>.

I pushed a fix that makes InnerObs part of SwitchMapOuterObserver via a PhantomData<fn() -> InnerObs> marker.

I also kept the reproduction coverage for Shared / Local, box_it, and box_it_clone, and cleaned up the test formatting.

Verified with:

cargo +nightly fmt --check
cargo test test_switch_map_box_it
cargo test

Hey, @M-Adoo. Thank you so much!