feat: add transfer hook helpers to the JS client

[dev-jodee]

Summary

Adds transfer hook support to the kit-based JS client as hand-written helpers in clients/js/src, porting the extra-account-meta resolution that previously only existed in clients/js-legacy. Closes #736.

• Codecs: ExtraAccountMeta and ExtraAccountMetaAccountData (with an Args type for encoding), plus EXECUTE_DISCRIMINATOR.
• Account and PDA helpers, following the generated client conventions: decodeExtraAccountMetaList, fetchExtraAccountMetaList, fetchMaybeExtraAccountMetaList and findExtraAccountMetasPda.
• Resolution: resolveExtraAccountMeta covering every address config — literal key, hook-program PDA, pubkey data (from instruction or account data) and external-program PDA — and every seed type (literal, instruction data, account key, account data); getExtraAccountMetasForExecute and addExtraAccountMetasForExecute, including the legacy client's privilege de-escalation.
• Instruction builders: getExecuteInstruction, getTransferCheckedWithTransferHookInstructionAsync and getTransferCheckedWithFeeAndTransferHookInstructionAsync, which fetch the mint, resolve the hook's extra accounts and append them (plus hook program and validation account) to the generated instruction. getTransferHookProgramId exposes the mint's active hook.

Behavior:

• Mints without a transfer hook, or with an inert one (programId unset), build the plain transfer instruction with no extra RPC calls.
• An active hook whose validation account does not exist throws SOLANA_ERROR__ACCOUNTS__ACCOUNT_NOT_FOUND, matching the Rust offchain helper. (The legacy JS client silently returns the instruction unchanged, which fails on-chain later.)
• Reserved discriminators 3..127 and truncated seed configs are rejected with explicit errors. (The legacy JS client crashes on the former and mis-resolves the latter.)

Tests

• test/extensions/transferHook/resolveExtraAccountMetas.test.ts — mock-RPC unit tests: validation account fetch/decode round-trip, every address-config discriminator including a chained external PDA, the with-fee builder, missing required account, missing validation account, invalid discriminator and truncated seed config.
• test/extensions/transferHook/transferCheckedWithTransferHook.test.ts — e2e against the test validator's spl-transfer-hook-example fixture: the builder resolves a fixed extra account and a seed-derived PDA, the transfer succeeds with the hook executing, and a transfer without the forwarded hook accounts fails with SOLANA_ERROR__INSTRUCTION_ERROR__MISSING_ACCOUNT.

pnpm test (tsc + ava, 140 tests) passes against the local test validator; eslint and prettier clean.

[amilz]

Looking good. I'm just wondering if some of this should get generated from the idl (IDK...just has me thinking)

[dev-jodee]

Looking good. I'm just wondering if some of this should get generated from the idl (IDK...just has me thinking)

Yeah, I'll post as a comment as well on the pr itself, but token-2022 is not the program that has the types ExtraAccountMetaList and Execute for Transfer Hook, it's https://github.com/solana-program/transfer-hook, so the idl isn't part of this repo. Choice was either to create a new package specific for transfer hook or to add it to the token-2022. I found the latter to make more sense and make it easier for devs, especially because transfer hook is part of 2022, but if that's not the preferred way, all good. We could also just add the ExtraAccountMetaList and Execute, to the IDL in this repo, but I'm not sure if it has precedence / if it's the style we want.