move allFutureThrowing helper to tests

[etan-status]

We use a generically seeming helper to help us track three Future exceptions throughout the entire codebase. Move the helper to tests where it finds more use. The helper has several design flaws that make it incompatible with {.async: (raises).} usage, and has the potential to swallow one of the three exceptions that we track with it.

The semantics should not change in this PR, this is a pure refactoring.

[codecov]

Codecov Report

Attention: Patch coverage is 93.75000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 82.77%. Comparing base (53e3825) to head (3ccb5c9).
Report is 2 commits behind head on unstable.

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #1037      +/-   ##
============================================
+ Coverage     82.75%   82.77%   +0.01%     
============================================
  Files            91       91              
  Lines         15616    15604      -12     
============================================
- Hits          12923    12916       -7     
+ Misses         2693     2688       -5     

Files	Coverage Δ
libp2p/errors.nim	66.66% <ø> (-7.15%)	⬇️
libp2p/stream/lpstream.nim	83.41% <100.00%> (ø)
libp2p/transports/tcptransport.nim	81.05% <100.00%> (+1.49%)	⬆️
libp2p/protocols/secure/secure.nim	71.42% <88.88%> (-1.30%)	⬇️

... and 3 files with indirect coverage changes

[arnetheduck]

this PR I guess is fine:ish but it does introduce a bit of unnecessary churn - it would be more clear if first, one annotated all close functions with raises - this would likely obsolete it entirely as most exceptions it protects against actually can't happen.

[etan-status]

Yeah, doing those next, but the problem is allFuturesThrowing doesn't work with {.async: (raises).} as the futures have different raises requirements and it doesn't use FutureBase.

So, getting rid of that problem first allows doing the close transition cleanly. Will do close next.