Feat 888 dotrain meta

[brusherru]

⚠️ This draft is based on rainlanguage/rain.metadata#74
For the development I've changed Cargo.toml to point on a local copy.
Before merging it should be reverted.

Motivation

It closes #888

Solution

It encodes DotrainOrderGui into DotrainInstanceV1 and adds it to the order's meta.
Also it implements function that parses meta data.

Still under development:

• front-end which will display possible and selected options (and a button "Deploy a copy"?)
• fetching of DotrainSourceV1 from Metaboard by hash

Publishing of DotrainSourceV1 is out of scope at the moment.

Checks

By submitting this for review, I'm confirming I've done the following:

• made this PR as small as possible
• unit-tested any new functionality
• linked any relevant issues or PRs
• included screenshots (if this involves a front-end change)

Summary by CodeRabbit

• New Features

  • Add-order flows (desktop, web, JS) can include optional GUI state as metadata; this is forwarded into calldata.
  • Orders expose parsed GUI metadata and a new API to fetch associated Dotrain source.
  • Order detail UI adds a State tab (GUI state JSON) and a Dotrain tab showing the Dotrain source.

• Improvements

  • Orders now parse and surface embedded metadata for richer UI experiences.
  • Better error messages when metadata or metaboards are missing or invalid.