fix(spraay): align tool ABI with the deployed contract

[plagtech]

Problem

The Spraay tool ABI merged in #95 declares four functions (spraayETH,
spraayToken, spraayETHVariable, spraayTokenVariable) whose selectors
do not exist in the deployed contract's bytecode
(0x1646452F98E36A3c9Cfc3eDD8868221E207B5eEC on Base), so every payment
call reverts at gas estimation. Two further issues surfaced while testing
the fix end to end: the "gas": 0 placeholder blocks estimation on the
default Base RPC, and using the confirmed (rather than pending) nonce makes
back-to-back sends collide.

All failures are loud and pre-broadcast — no funds were ever at risk, and
the contract has no on-chain record of calls to the missing selectors.

Fix

• ABI replaced with the verified deployed interface (copied verbatim from
  the Sourcify-verified source): sprayEqual(token, recipients, amount)
  for equal sends (address(0) = ETH), and sprayETH / sprayToken with
  Recipient[] structs for variable sends
• Protocol fee read live from feeBps() (owner-adjustable on-chain) with
  a safe fallback
• Gas: build_transaction estimates (no zero placeholder), then a 10%
  buffer is applied
• Nonce: fetched with "pending" so sequential sends don't collide

No public API changes: tool names, signatures, and return shapes are
unchanged, so existing agents need no code changes.

Verification

• 25/25 unit tests, including new ABI-shape regression tests that pin the
  ABI to the verified contract interface
• Selector pre-flight: every declared function's selector confirmed present
  in the deployed bytecode
• Mainnet transactions through the fixed tools on Base:
  • 0x8701665d9ef5c99c14d548e89f5f4fa3eab0ff0841d696adff33f0a3be83e1ff (sprayEqual)
  • 0x795ff187a8426ff0c2439fefd2339e0ab5105a349a900dac5e9b7b8fb11a7507 (sprayEqual)
  • 0xa93e4b1b0ab99a30bcb3607190954e89ed15d09dc52c61e23e088805c4f27700 (sprayETH,
    variable amounts — consecutive block with the previous tx, exercising the
    sequential-send path)

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