feat: add a Morphir IR to WIT backend

[DamianReeves]

Part of finos/morphir#958, phase B.

What

Add a backend that turns Morphir IR types into a WIT package. No such backend exists in this repo. The earlier Go pipeline moved to finos/morphir-go.

• Records, custom types, Maybe, Result, List and Dict map to WIT records, variants, options, results and lists.
• WIT has no recursive types. The backend rejects them, or encodes them as morphir:ir encoded-ast does.
• The package name and version come from the model, for example morphir:mep@0.1.0.
• Do not use error-context.

Done when

• The MEP model produces a WIT package that wasm-tools component wit accepts.
• A recursive type gets a clear diagnostic or the documented encoding.

Design

checkpoint 7, checkpoint 9 in finos/morphir#949.

[DamianReeves]

Tracking moved to beads: morphir-opua.1.2.4 in the finos/morphir repository's .beads database. This issue stays open as a mirror and links there.