feat(sdk): generate MEP protocol types from the MEP model IR

[DamianReeves]

Part of finos/morphir#958, phase B.

What

Commit a copy of the MEP IR from an exact finos/morphir commit, with its source and digest:

vendor/morphir-mep/ir.json   # source: finos/morphir spec/mep @ <sha>, sha256: ...

Generate the Rust protocol types in morphir-extension-sdk from it with the morphir-rust backend. When model publishing exists, the copy becomes morphir package restore.

Done when

• The generated types replace the hand-written protocol types, and the wire format is unchanged.
• CI fails when the generated Rust does not match the vendored IR.

Blocked by

• feat(spec): add spec/mep with the MEP contract as a Gleam model morphir#964

Design

checkpoint 9, checkpoint 12 in finos/morphir#949.

[DamianReeves]

Tracking moved to beads: morphir-opua.1.2.2 in the finos/morphir repository's .beads database. This issue stays open as a mirror and links there.