Cardano Updates

Export ToChoosable(toChoice) and add choiceFromList

Codebase cleanup

Rework custom validators to work with generic rules

New Huddle example `tagRangeExample`: `foo<a> = #6.1280(a) / #6.1400(a)`
used at `[foo<uint>, foo<nint>]`, with a custom generator that picks any
tag in `1280..1400` (biased toward the edges via `frequency`) and a
custom validator accepting the same range. Both delegate to the bound
generic type via `generateFromGRef` / `validateFromGRef`.

Wired into the `Generated value validates` round-trip suite, plus a
separate property that classifies tag samples to surface edge
coverage (33% edge / 67% middle).

Custom generators and validators attached to a generic Huddle rule can
now look up the type bound to a generic parameter at the enclosing
rule. Add `generateFromGRef` and `validateFromGRef` helpers, plus
`validateFromName`. Custom closures attached to generic rules are
wrapped at monomorphization time to install the active local bindings
into `geLocal`/`veLocal` on `GenEnv`/`ValidateEnv`, which a new
`lookupGRef` method on `MonadCddl` consults.

`runCBORValidator` now takes a `CTreeRoot ValidatorPhase` directly.
`GRef` moves to `Codec.CBOR.Cuddle.CDDL` so lower-level modules can
use it; `Huddle` re-exports it without the constructor.