fix(core/subscribe): stop rendering children when source$ switches

[voliva]

I had an issue caused because I was receiving the old value from a factory bind(id => ...) when switching its key based on a router's param.

We realised this shouldn't happen when using Subscribe boundaries properly, but Subscribe doesn't currently handle the case of the source stream switching.

In here I add two tests: The first one tries to represent the underlying issue in Subscribe, but it turned out really contrived. So I also added a second test which better represents the issue I was having initially.

[codecov]

Codecov Report

Merging #147 (8b96080) into main (90e6a00) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #147   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           22        22           
  Lines          342       349    +7     
  Branches        41        43    +2     
=========================================
+ Hits           342       349    +7     

Impacted Files	Coverage Δ
packages/core/src/Subscribe.tsx	100.00% <100.00%> (ø)
packages/core/src/bind/connectFactoryObservable.ts	100.00% <100.00%> (ø)
packages/core/src/bind/connectObservable.ts	100.00% <100.00%> (ø)
packages/core/src/internal/useObservable.ts	100.00% <100.00%> (ø)

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[josepot]

Thanks a lot for this @voliva ! I've added a bunch of commits with tiny improvements. Please, could you please re-review it before we merge?