test: proptest Type validation and substitution

[acl-cqc]

• Add proptest::Strategys that produce valid/well-formed Types/etc.
  • CustomTypes being correct wrt. the TypeDef's in the ExtensionRegistry passed in
  • such that any TypeArgs are correct for the TypeParams into which they must fit (e.g. in those TypeDefs)
  • containing variables, with the strategy also returning an appropriate "environment" i.e. Vec<TypeParam> declaring all variables that are used
  • (all this done by a fold or "State monad"-like mechanism of passing in an environment to each Strategy that then returns a copy of that environment with potentially more variables.)

Using std_reg(), thus produce types and valid substitutions for the variables in those types; check the type is valid in the original environment, and after substitution, is valid in the environment for the substituted-in values.

Coverage of making TypeArgs for TypeParam::{List, Tuple, Extensions} is missing because the std_reg() does not declare any types taking those kinds of type arguments (!)....hence, TODOs:

• add/generate row variables, this should give coverage of TypeParam::List
• add some tests with strategies that prop_filter for "interesting" cases, to check such are actually generated. This may allow tweaking/improving probabilities/distributions.
• decide how to organise code. Question: what do folks think about removing old Type proptests (should be subsumed by this, but potentially simpler/easier-to-understand)

And, extend this to test substitution of nodes/operations - in time, that will probably be a second PR.

[codecov]

Codecov Report

Attention: Patch coverage is 82.10117% with 46 lines in your changes missing coverage. Please review.

Project coverage is 86.64%. Comparing base (21ac35c) to head (c43062b).
Report is 23 commits behind head on main.

Files with missing lines	Patch %	Lines
hugr-core/src/types.rs	82.03%	46 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1744      +/-   ##
==========================================
+ Coverage   86.52%   86.64%   +0.11%     
==========================================
  Files         188      192       +4     
  Lines       34205    35021     +816     
  Branches    31076    31834     +758     
==========================================
+ Hits        29597    30343     +746     
- Misses       2923     2976      +53     
- Partials     1685     1702      +17     

Flag	Coverage Δ
python	92.31% <ø> (-0.28%)	⬇️

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[acl-cqc]

Here's an example:

• original type TypeBase(Extension(CustomType { extension: IdentList("collections.list"), extension_ref: (Weak), id: "List", args: [Type { ty: TypeBase(Variable(0, Any), Any) }], bound: Any }), Any)
• original environment [Type { b: Any }]
• Substituted variable 0: Type { ty: TypeBase(Sum(General { rows: [TypeRowBase { types: [TypeBase(Function(FuncTypeBase { input: TypeRowBase { types: [TypeBase(Extension(CustomType { extension: IdentList("prelude"), extension_ref: (Weak), id: "usize", args: [], bound: Copyable }), Copyable)] }, output: TypeRowBase { types: [TypeBase(Variable(0, Any), Any)] }, runtime_reqs: ExtensionSet({IdentList("logic")}) }), Copyable), TypeBase(Extension(CustomType { extension: IdentList("prelude"), extension_ref: (Weak), id: "qubit", args: [], bound: Any }), Any), TypeBase(Extension(CustomType { extension: IdentList("arithmetic.float.types"), extension_ref: (Weak), id: "float64", args: [], bound: Copyable }), Copyable)] }] }), Any) }
• result: TypeBase(Extension(CustomType { extension: IdentList("collections.list"), extension_ref: (Weak), id: "List", args: [Type { ty: TypeBase(Sum(General { rows: [TypeRowBase { types: [TypeBase(Function(FuncTypeBase { input: TypeRowBase { types: [TypeBase(Extension(CustomType { extension: IdentList("prelude"), extension_ref: (Weak), id: "usize", args: [], bound: Copyable }), Copyable)] }, output: TypeRowBase { types: [TypeBase(Variable(0, Any), Any)] }, runtime_reqs: ExtensionSet({IdentList("logic")}) }), Copyable), TypeBase(Extension(CustomType { extension: IdentList("prelude"), extension_ref: (Weak), id: "qubit", args: [], bound: Any }), Any), TypeBase(Extension(CustomType { extension: IdentList("arithmetic.float.types"), extension_ref: (Weak), id: "float64", args: [], bound: Copyable }), Copyable)] }] }), Any) }], bound: Any }), Any)
  Which is to say, List<Var(0)> substituted with variable 0 = some-crazy-sum produces List<some-crazy-sum>, ho hum.