Fix Arbitrary instance and invariant checking for Proposals

[lehins]

Description

• Fix flaky cddl test triggered on CI
• Fix invalid fallback implementation of Mirror downloading, which made into a flake setop on CI resulting in this failure
• Fix flaky proposal tests that happened here and here. More on that below

Fix test data generation and improve invariant checking:

• Fix Arbitrary instance for Proposals:

  • Allow empty to be generated
  • Generate InfoAction and TreasuryWithdrawal

• Remove proposalsAreConsistent in favor of toPForest. Besides
  checking the invariant it also constructs a forest of Trees that
  can be used for debugging.

• Invariant checking improved:

  • Remove invariant that pProps domain should equal to all children
    and that domain of pGraph equals to the domain of pProps
  • Enforce that all children are uniqe and that parents are correctly
    specified and matches the inverse relation from a parent to the
    child

toPForest not only checks the invariant, but serves as a nice debugging tool, since it allows us to print the hierarchy in a readable fashion, eg.:

{pfPParamUpdate =
x
, pfHardFork =
x
|
+- be4eaa8cc3a8e95fd0d02daaa55705a467f1327392dd7ea3749d128b8e0815c5#671359595
|
`- c0a4ef9bfeb257488525de250468e24b3c6340a6872ef366877c46a28a842c37#1165802016
   |
   `- 6cad5468f5320b34d411913292c2a40b1258fa11c7d5eecff6ad4b7325285422#1412147132
, pfCommittee =
a3e6fc1f9eec9a66c5ee56819f4a93658f6d018ef74d991d6d25242b8915d163#104556382
|
+- e6d969f5d7f10a8681aa8f9cf42328e98aaf653ec00353f340f37397c8181378#402911737
|  |
|  `- bca38b2ec2b04afb4d6fa61f3f1b8d5f3fbc77646626e4e7998b141cb41421fc#1225600682
|
`- e718c251f603af13b459fb22c4c0c0fdf03452ac06a3dbf45653ee87ce1c6ca7#1350459191
, pfConstitution =
f829acfb70d5a73396db0b1de29e34053cf80475b69382c9f390aef21e82d58a#767672592
|
`- 51f119927ec29d32df70c4bd90ba47b9542e59394ec9d8d5f8ffa1faebc56424#3360066490
   |
   +- 66a72530e4e79424a584e6f92f5a040f3b7122192622d06969e9318f4e5b49b8#45552015
   |
   +- 68b88d61580ee03573e0162a7546d1b5928b5798dad719ee40d2a801c77f279a#2339408668
   |
   `- dd04849e45e40f23775c0db04652641d8257593a7f5186625e3c836da57ecf66#179964133
}

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated
• When applicable, versions are updated in .cabal and CHANGELOG.md files according to the
  versioning process.
• The version bounds in .cabal files for all affected packages are updated. If you change the bounds in a cabal file, that package itself must have a version increase. (See RELEASING.md)
• All visible changes are prepended to the latest section of a CHANGELOG.md for the affected packages. New section is never added with the code changes. (See RELEASING.md)
• Code is formatted with fourmolu (use scripts/fourmolize.sh)
• Cabal files are formatted (use scripts/cabal-format.sh)
• hie.yaml has been updated (use scripts/gen-hie.sh)
• Self-reviewed the diff

[aniketd]

Super awesome! 💯 🙌