Replace viem with existing ethereumjs dependencies in sdk-coin-tempo

[Copilot]

The sdk-coin-tempo module introduced viem as a dependency for Ethereum utilities (address validation, ABI encoding, unit conversion). This adds unnecessary weight when equivalent functionality exists in ethereumjs-util, ethereumjs-abi, and bignumber.js - already used throughout the monorepo.

Changes

Removed viem dependency

• Removed viem from package.json
• Added ethereumjs-util, ethereumjs-abi, bignumber.js (versions match abstract-eth)

Type definitions (src/lib/types.ts)

• Address and Hex types: viem imports → custom type aliases (string)

Utility functions (src/lib/utils.ts)

• Address validation: viem.isAddress() → ethereumjs-util.isValidAddress()
• Unit conversion: viem.parseUnits()/formatUnits() → BigNumber-based implementations
• ABI encoding: viem.encodeFunctionData() → ethereumjs-abi.methodID() + rawEncode()
• Buffer/hex ops: viem.pad()/toHex() → ethereumjs-util.setLengthRight()/bufferToHex()

Test files

• Address checksumming: viem.getAddress() → ethereumjs-util.toChecksumAddress()

Example

Before:

import { parseUnits, encodeFunctionData, isAddress } from 'viem';

const amount = parseUnits('1.5', 6);
const data = encodeFunctionData({
  abi: TIP20_ABI,
  functionName: 'transferWithMemo',
  args: [to, amount, memo]
});

After:

import EthereumAbi from 'ethereumjs-abi';
import { isValidAddress, bufferToHex } from 'ethereumjs-util';
import BigNumber from 'bignumber.js';

const amount = BigInt(new BigNumber('1.5').multipliedBy(1e6).toFixed(0));
const methodId = EthereumAbi.methodID('transferWithMemo', types);
const args = EthereumAbi.rawEncode(types, [to, amount.toString(), memo]);
const data = bufferToHex(Buffer.concat([methodId, args]));

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