Adopt spec entry ids and id-based reference resolution

[leighmcculloch]

Note

Part of a stack of PRs that must merge in this order.

A first group of PRs deliver const-encoded contract specs, so that contract specs are produced at compile time instead of at proc-macro execution time. This provides the foundation for the capability to construct the specs from information that is not known at proc-macro execution and only known at compile time, like the fully qualified name of a type:

1. Add borrowed Ref variants of generated types rs-stellar-xdr#560
2. Add const XDR serialization on View types rs-stellar-xdr#562
3. Encode contract spec XDR at const evaluation time rs-soroban-sdk#1965

A second group of PRs deliver ids on contract spec entries and in spec references. Every entry carries an 8-byte id hashed from the fully qualified name of the item it describes, and a reference to a user-defined type carries the id of the entry it refers to, so references stay unambiguous even when items share a name. This resolves the type identity problem (stellar/rs-soroban-sdk#1570) and type alias limitations (stellar/rs-soroban-sdk#1857):

1. Add ids to contract spec entries stellar-xdr#313
2. Regenerate with ids on contract spec entries rs-stellar-xdr#568
3. Add ids to contract spec entries rs-soroban-sdk#1998
4. Adopt spec entry ids and id-based reference resolution #2677 ← this PR

What

Patch stellar-xdr to stellar/rs-stellar-xdr#568 and the soroban spec crates to stellar/rs-soroban-sdk#1998, moving the workspace to stellar-xdr 28 and soroban-env-host 28.0.1, and adapt the CLI to specs whose entries carry ids:

• soroban-spec-tools' Spec normalizes v2 entries on construction — each entry's v0 body is stored so all consumers keep matching one shape — and keeps each entry's id keyed to its body. A ScSpecTypeUdtv2 reference resolves through find_udt_v2: the entry whose id matches when one does, exactly even when entries share a name, falling back to the referenced name for specs of v0 entries.
• Spec verification and TypeScript bindings treat a v2 entry as its body plus an identity.
• The CLI handles the new ScVal::ExecutableTag and ContractExecutable::ExternalRef variants.

Why

Contract spec entries now carry an id hashed from the fully qualified name of the item they describe, and references to user-defined types carry the id of the entry they refer to. The CLI has to read, print, and generate bindings from specs produced by SDKs that emit them — and with ids it can resolve a reference to exactly the entry it was written against.

Known limitations

Merging depends on the upstream PRs landing and releasing, with the [patch.crates-io] git revisions replaced by published versions. Network-backed test suites need a quickstart image running a protocol 28 host.