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.

[brice-stacks]

LGTM, but there are some clippy issues preventing the tests from running.

[jcnelson]

LGTM; just please add copyright comment blocks 🙏

[codecov]

Codecov Report

❌ Patch coverage is 42.85714% with 112 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.14%. Comparing base (3da96c1) to head (9c6a2ff).

Files with missing lines	Patch %	Lines
...tackslib/src/chainstate/stacks/tests/reward_set.rs	28.08%	105 Missing ⚠️
stacks-node/src/tests/signer/v0.rs	0.00%	7 Missing ⚠️

❌ Your project check has failed because the head coverage (68.14%) is below the target coverage (80.00%). You can increase the head coverage or adjust the target coverage.

❗ There is a different number of reports uploaded between BASE (3da96c1) and HEAD (9c6a2ff). Click for more details.

HEAD has 21 uploads less than BASE

Flag	BASE (3da96c1)	HEAD (9c6a2ff)
	88	67

Additional details and impacted files

@@             Coverage Diff              @@
##           develop    #6640       +/-   ##
============================================
- Coverage    78.18%   68.14%   -10.04%     
============================================
  Files          580      582        +2     
  Lines       361096   361289      +193     
============================================
- Hits        282312   246208    -36104     
- Misses       78784   115081    +36297     

Files with missing lines	Coverage Δ
stackslib/src/chainstate/stacks/tests/mod.rs	77.24% <ø> (-3.71%)	⬇️
stackslib/src/lib.rs	100.00% <ø> (ø)
stackslib/src/proptest_utils.rs	100.00% <100.00%> (ø)
stacks-node/src/tests/signer/v0.rs	14.83% <0.00%> (-6.50%)	⬇️
...tackslib/src/chainstate/stacks/tests/reward_set.rs	28.08% <28.08%> (ø)

... and 339 files with indirect coverage changes

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