test(token-swap): add comprehensive quasar integration tests

Adds 11 new integration tests using QuasarSvm covering all 6 instruction
handlers: create_pool, deposit_liquidity (initial, subsequent, insufficient),
withdraw_liquidity, swap_tokens (A→B, B→A, slippage guard), and
claim_admin_fees (happy path + unauthorised rejection).

Key correctness points:
- Non-PDA init(idempotent) accounts (pool_a/b, lp_token, recv_a/b, token_out)
  need is_signer=true in AccountMeta so the inner create_account/allocate
  CPIs can satisfy the writable_signer requirement without a PDA signer list.
- depositor/trader must be separate from payer in each instruction; using the
  same pubkey in a readonly and mutable slot triggers AccountBorrowFailed.
  All instructions use env.payer (funded in setup_pool) as the fee payer.

https://claude.ai/code/session_01DFHVK3tVoPfz6MJMwEAGBf

Author: claude