create fast environment package

[frrist]

Wat

This PR repackages the way FAST is laid out to make it more friendly to work with deps
This PR adds GetFunds to the environment interface and modifies DevNet and MemoryGenesis to impl it.

[codecov-io]

Codecov Report

Merging #2919 into master will decrease coverage by 1%.
The diff coverage is 6%.

@@           Coverage Diff            @@
##           master   #2919     +/-   ##
========================================
- Coverage      43%     41%     -2%     
========================================
  Files         210     136     -74     
  Lines       12466    8278   -4188     
========================================
- Hits         5389    3436   -1953     
+ Misses       6262    4259   -2003     
+ Partials      815     583    -232

Impacted Files	Coverage Δ
tools/fast/fastesting/basic.go	0% <0%> (ø)	⬆️
tools/fast/environment/environment_devnet.go	0% <0%> (ø)
...ols/fast/environment/environment_memory_genesis.go	0% <0%> (ø)
tools/fast/process.go	38% <33%> (-1%)	⬇️
tools/fast/process_stderr_recorder.go	70% <80%> (-1%)	⬇️
tools/migration/internal/test_helpers.go	0% <0%> (-100%)	⬇️
core/message_pool.go	0% <0%> (-95%)	⬇️
core/message_queue.go	0% <0%> (-92%)	⬇️
protocol/hello/hello.go	2% <0%> (-87%)	⬇️
tools/migration/internal/runner.go	0% <0%> (-86%)	⬇️
... and 88 more

[anorth]

Implementation looks ok but the intent is totally opaque, so please expand on documentation before landing.

[anorth]

This needs more explanation. The method only returns an error, so what does "get" mean? From where are they got? Where is the fixed amount specified? Are they guaranteed to have landed when this method returns?

Edit: having now read implementation, it would probably be better to be more explicit and call this RequestFaucetFunds or similar. The questions above still stand.