Expose validated RGB transfer and contract imports

[Jainakin]

Summary

Rebase validated contract and transfer-consignment metadata import onto RLN v0.13.0-beta.3 (af03c7f1a65135a429f05a5820600338215954dc). The existing SDK, HTTP, UniFFI and C-FFI APIs share one parser and mutation path.

The released RGB-lib v0.3.0-beta.34 already includes contract-only import. This revision keeps the release's root Cargo manifest, lockfile and rust-lightning gitlink unchanged. The old RGB-lib and rust-lightning fork overrides are removed. No VSS changes from the newer dev tip are included.

Semantics and safety

• Contract import validates the public contract and expected asset identity before registering metadata. It creates no allocations or asset balance.
• Transfer-consignment import registers metadata for an already accepted transfer. It is not ownership acceptance or a replacement for normal on-chain receiving.
• Strict standard Base64; maximum 16 MiB of encoded text (at most 12 MiB decoded), with bounded HTTP bodies.
• Exact transaction-ID parsing and canonical metadata responses.
• Parsing and wallet mutation run on blocking workers. Submitted mutations retain lifecycle ownership through completion even if the caller stops waiting.
• Contract idempotence and interrupted-persistence repair come from released RGB-lib. Attachment-bearing standalone contracts require a separate flow providing their files.

Verification

Rebased head: 5d5aa742984d52767e1055fed6aa154ad732d551. The local Rust funded test ran at implementation commit 6300718; the follow-up changes formatting only. Downstream native builds include the current 5d5aa74 import source.

• Locked SDK test compile with UniFFI, test utilities and VLS: passed.
• Real regtest SDK import test: passed, 39.84 seconds, against the existing Core 31.1 / Electrs 0.12 / proxy 0.3 qualification stack, using loopback port/auth adapters without recreating services.
• That test covers NIA and IFA contract import, expected-ID mismatch before mutation, canonical metadata, zero initial balance, duplicate import, a fresh IFA-specific invoice, receipt of 250,000 real fixture units, issuer/recipient spendable balances, and reimport preserving allocations.
• Strict Base64 parsing unit test: passed.
• UniFFI entrypoint, identity, error and signing tests: 10 passed.
• Rust formatting and diff whitespace checks: passed.

Downstream integration is pushed in Node #23, Bare #21, WDK #44 and Iris #8. Both Node and Bare pass fresh imported-IFA receipt/send/settlement and balance-preserving reimport. WDK passes 706 tests; Iris passes 2384 tests, Android APK checks and the signed iOS simulator app build/identity checks. Initial iOS normal authentication, native baseline and BTC address generation pass; the Mac relocked before funded app tests. All five Node native runtime jobs and all seven Bare source/ABI builds pass. Bare's two Android 64-bit jobs fail the existing published-linker post-packaging RELRO gate, not native source compilation.

PR CI checks the dev merge 1bd104750a65821ab9880f8f9edfb36bceba16fd, not the raw production-rebased head. Core/SDK, external signer, language bindings, feature matrix, platform builds, general test/coverage and persistence sanitizer checks pass. The VSS test job fails restored_node_recovers_force_closed_channel_funds: balance remains zero with missing/spent-input diagnostics. This merge includes newer dev VSS changes that the downstream production-based builds do not include. Root cause is unassigned pending baseline comparison; the failure is not waived.

Earlier branch-head platform results are not qualification of this rebase. C-FFI consumers still require the binding/build adapter maintained in the binding packages.

The fixture asset is regtest-only and is not production USDT. This PR does not establish Signet/mainnet deployment readiness or resolve unrelated signer-lock, VSS or recovery issues.