stdlib: add property based testing

[saem]

Summary

Introduces property based testing via the property_testing module under the experimental part of the standard library.

Details

• info that couldn't fit into the summary
• relevant details; tricky parts
• anything else

---

Notes for Reviewers

• clean-up of the api:
  • split into:
    • substitutable random number generation, with skipping, etc
    • arbitrary infrastructure and core definitions and mapping/filtering
    • create a test library with "manual" API, and possibly separately a test runner
• allow for substituting rngs via an interface object
• implement minimizing:
  • should we keep the shrinkable concept, or drop shrinking until later?
• clean-up docs
• write a proper commit message

[saem]

The output from the current tests looks as follows, each property has an id that should be useable to run it specifically in the future:

nim

1 uint32
- are >= 0 (id: 1) - status: success, totalRuns: 1000
- within the range[100000000, 4294967295] (id: 2) - status: success, totalRuns: 1000

1.1 enums
- are typically ordinals (id: 3) - status: success, totalRuns: 1000

1.2 characters
        1.2.1 are ordinals
        - forming a bijection with int values between 0..255 (inclusive) (id: 4) - status: success, totalRuns: 1000
        - have successors and predecessors or are at the end range (id: 5) - status: success, totalRuns: 1000

- ascii - are from 0 to 127 (id: 6) - status: success, totalRuns: 1000

1.3 strings
- concatenation - len is == the sum of the len of the parts (id: 7) - status: success, totalRuns: 1000

1.4 sets
- cannot contain more items than the enum itself (id: 8) - status: success, totalRuns: 1000
        1.4.1 union
        - a union of sets contain all elements of each (id: 9) - status: success, totalRuns: 1000
        - union is commutative (id: 10) - status: success, totalRuns: 1000

        1.4.2 intersection
        - an intersection is a subset of both operands (id: 11) - status: success, totalRuns: 1000
        - intersection is commutative (id: 12) - status: success, totalRuns: 1000

        1.4.3 difference (or relative complement)
        - a difference has no overlap with the second operand (id: 13) - status: success, totalRuns: 1000

[saem]

Using the following doc to discuss the CLI interface for PBT: https://gist.github.com/saem/3df20c8afa67bc4c266dbe2dfa21e2b5