eds: add BurnMintFactory URL resolution for utility-registry instruments

[stackman27]

Summary

Adds URL-based factory resolution (FactoryTypeURL) for BurnMintTokenPool, enabling CCIP bridging for Splice utility-registry instruments whose factory contracts don't have an instanceId field and thus can't be resolved via the existing
FactoryTypeAddress branch.

Problem

The EDS's getBurnMintFactory only supported FactoryTypeAddress, which calls acs.Get(InstanceAddress) against the local ACS store. This requires the factory contract to have an instanceId create-arg field (used to compute
keccak256(instanceId@party) for address indexing).

Utility-registry factory contracts (e.g. AllocationFactory from utility-registry-app-v0) have create args {operator, provider, registrar} — no instanceId field. They're silently dropped from the address index (getInstanceAddresses in
active_contract_store.go requires instanceId), so acs.Get misses and the burn-mint-factory context key is never populated. The pool's lookupBurnMintFactory aborts with:

Missing context entry for: burn-mint-factory

Additionally, AllocationFactory_InternalBurnMint reads instrument-configuration and issuer-credentials from the choice context (extraArgs.context.values). The existing FactoryTypeAddress branch returns empty ChoiceContext{}, so even
if the factory were findable by address, the choice would fail on missing instrument config + credentials.

Solution

Config schema (eds/config/config.go)

• Added TokenStandardURL + TokenStandardAuthConfig fields to BurnMintFactory (mirrors TransferFactory's existing URL fields)
• Extended validate tag: oneof='' address → oneof='' address url

Resolver (eds/internal/api/tokenpool/token_standard.go)

• Implemented FactoryTypeURL branch: calls DA's utility-registry backend endpoint via HTTP, parses FactoryWithChoiceContext response (factoryId + choiceContext.choiceContextData + choiceContext.disclosedContracts)
• Changed burnMintFactory function signature to return (string, ChoiceContext, []DisclosedContract, error) — mirroring transferFactory — so the credentials and instrument config returned by the backend can flow through to the pool's
  context
• Uses /mint/v0/request endpoint (read-only, does not actually mint) because DA's /burn-mint-factory endpoint currently has a bug returning issuer-credentials: []. Both endpoints return the same factoryId (AllocationFactory) and the same
  context keys. Revisit when DA fixes /burn-mint-factory — switch token_standard_url config to the burn-mint-factory path and change the request body shape.

Call sites (eds/internal/api/tokenpool/tokenpool.go)

• Updated both send + execute paths to handle the new 4-return signature
• Merge factory-returned ChoiceContext.Values (including issuer-credentials + instrument-configuration) into burnMintFactoryContext, which gets promoted to choiceContext["burn-mint-factory-extra-args-values"] by existing code — the
  context key the pool reads at BurnMintTokenPoolV2.daml:87-97

Tests (eds/config/config_validation_test.go)

• Added validation test cases for FactoryTypeURL (valid + missing URL)

Config example

[token_pool_api.token_pools."<pool address>"]             
  type             = "burnMint"                                                                                                                                                                                                                      
  party_id         = "<registrar party>"                                                                                                                                                                                                             
  instance_address = "<pool address hex>"                                                                                                                                                                                                            
  pool_owner       = "<registrar party>"                                                                                                                                                                                                             
                                                                                                                                                                                                                                                     
  [token_pool_api.token_pools."<pool address>".burn_mint_factory]                                                                                                                                                                                    
    type               = "url"                                                                                                                                                                                                                       
    token_standard_url = "https://api.utilities.digitalasset-staging.com/api/utilities/v0/registry/mint/v0/request"                                                                                                                                  
    # token_standard_auth — NOT set, DA's endpoint is public (security: [])