[indexer]: index solana ismp host events

[dharjeezy]

Summary

• Adds a third solana branch to the indexer config schema, manifest template, and codegen, so a Solana ISMP host slots into the multichain SubQuery project the same way EVM and Substrate hosts do.
• Wires three handlers against the real PR [solana]: Host, Handler and Verifier Programs #801 host program: storeStateCommitment (= EVM StateMachineUpdated), dispatchIncoming (= EVM PostRequestHandled), and vetoStateCommitment (logs at WARN until the GraphQL schema gains a vetoed flag).
• Inbound-only by design, matching the host program. No outbound dispatch indexing, no timeout handlers.

Background

PR #801 (royvardhan/solana-ismp-host) ships the Hyperbridge host program for Solana.

The host has no Anchor #[event]s, so every indexable surface is an InstructionHandler filtered by Anchor discriminator (camelCase function name from the IDL). The instruction params carry state_root, overlay_root, and timestamp directly, so the handler decodes the commitment from the params rather than fetching the [b"commit", state_machine_u32_le, height_u64_le] PDA after the fact.

What has been done so far

• src/configs/index.ts: Zod solana branch with ismpHost / tokenGateway / intentGateway base58 program ids plus an optional quorum policy
  (providers, threshold) and a refinement that rejects threshold > providers.length.
• scripts/templates/solana-chain.yaml.hbs: Handlebars template emitting a solana/Runtime data source per program. Three InstructionHandler entries on the host program (storeStateCommitment, dispatchIncoming, vetoStateCommitment), conditional blocks for token and intent gateways for forward compatibility.
• scripts/generate-chain-yamls.ts: generateSolanaYaml (uses getSlot at commitment: "finalized" for the local-env live head, static startBlock elsewhere), config.type dispatch in generateAllChainYamls, and Solana-aware sidecar generators (chains-by-ismp-host, gateway-address maps).
• src/handlers/events/solana/storeStateCommitment.instruction.handler.ts: decodes StoreStateCommitmentParams, derives source-chain id (POLKADOT-${u32} on mainnet), writes StateMachineUpdateEvent.
• src/handlers/events/solana/dispatchIncoming.instruction.handler.ts: decodes DispatchIncomingParams, pulls relayer pubkey from instruction account index 1,
  calls RequestService.updateStatus({ status: Status.DESTINATION }) keyed by the 32-byte commitment.
• src/handlers/events/solana/vetoStateCommitment.instruction.handler.ts: logs at WARN. See doc section 5.5 for why we don't write a row yet.
• src/utils/solana.helpers.ts: hand-written decoders for StoreStateCommitmentParams and DispatchIncomingParams. No Borsh runtime dep; the layouts are short and fixed-size.
• src/services/stateMachine.service.ts: createSolanaStateMachineUpdatedEvent. Receives the commitment in args (no fetch) since the instruction params carry
  it.
• src/types/subql-solana.ts: local SolanaInstruction interface which will be replaced when @subql/types-solana is added.
• src/mappings/mappingHandlers.ts: re-exports the three handlers under their YAML-bound names.

Depends on #801.