[LesterEvSe]

Motivation

When types are resolved, builtin aliases turn into their underlying types: Pubkey, Fe and Scalar become u256, and Point becomes (u1, u256). So AbiMeta can't tell a public key from an arbitrary 256-bit number.

Simplex needs this information for correct, strongly typed include_simf expansion and simplified fuzz value generation. Its entire inner structure depends on values derived from the ResolvedTypes in AbiMeta.

Note: the tag is metadata, not part of the type. PartialEq, Eq and Hash are now implemented by hand and ignore it, so Pubkey and u256 stay interchangeable and type checking is unchanged.

Also added minor refactoring in types/README.md missing from ast refactoring

Checklist

• If this PR adds or changes a language feature, it is used in
  examples/kitchen_sink.simf, and test-data/kitchen_sink.json is
  regenerated.

[KyrylR]

ACK d600cac; successfully ran local tests

note on metadata retention: when a parameter's first analysed use carries the plain structural annotation, a later Pubkey-typed or jet-inferred use does not update the stored tag, including nested array elements

There are two small follow-ups from what I can see:

1. Fix a note above, it is non-blocking for this PR imo
2. Also noticed that we have a stale README nominal-typing sentence in src/types/README.md:20, also can be fixed later

[apoelstra]

ACK d600cac; successfully ran local tests; this is fine.