Property Tests: make_reward_set proptest and documentation

[aaronb-stacks]

This PR adds some docs for how we should handle property testing in this repo going forward, and it includes an example property test for the make_reward_set function.

[CLAassistant]

All committers have signed the CLA.

[codecov[bot]]

Codecov Report

:x: Patch coverage is 75.25773% with 48 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 73.05%. Comparing base (3da96c1) to head (955f4ac). :warning: Report is 47 commits behind head on develop.

Files with missing lines	Patch %	Lines
stackslib/src/proptest_utils.rs	0.00%	43 Missing :warning:
stacks-node/src/tests/signer/v0.rs	0.00%	5 Missing :warning:

:x: Your project status has failed because the head coverage (73.05%) is below the target coverage (80.00%). You can increase the head coverage or adjust the target coverage.

:exclamation: There is a different number of reports uploaded between BASE (3da96c1) and HEAD (955f4ac). Click for more details.

HEAD has 25 uploads less than BASE

Flag	BASE (3da96c1)	HEAD (955f4ac)
	88	63

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #6640      +/-   ##
===========================================
- Coverage    78.18%   73.05%   -5.13%     
===========================================
  Files          580      582       +2     
  Lines       361096   361458     +362     
===========================================
- Hits        282312   264056   -18256     
- Misses       78784    97402   +18618     

Files with missing lines	Coverage Δ
stackslib/src/chainstate/stacks/tests/mod.rs	80.94% <ø> (ø)
...tackslib/src/chainstate/stacks/tests/reward_set.rs	100.00% <100.00%> (ø)
stackslib/src/lib.rs	100.00% <ø> (ø)
stacks-node/src/tests/signer/v0.rs	14.91% <0.00%> (-6.42%)	:arrow_down:
stackslib/src/proptest_utils.rs	0.00% <0.00%> (ø)

... and 269 files with indirect coverage changes

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