transaction-controller: reject transactions with both gasPrice and EIP-1559 fee fields instead of gracefully preferring maxFeePerGas

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## Bug Description

`validateGasFeeParams` in `@metamask/transaction-controller` throws when a transaction includes both `gasPrice` and `maxFeePerGas`/`maxPriorityFeePerGas`, even when the transaction `type` is explicitly `0x2` (EIP-1559). Instead of stripping the redundant `gasPrice` and proceeding, MetaMask rejects the transaction entirely.

## Steps to Reproduce

Some RPCs return `gasPrice` alongside EIP-1559 fee fields. For example, Arbitrum's `eth_fillTransaction`:

```bash
curl -s -X POST https://arbitrum-one.publicnode.com \
-H "Content-Type: application/json" \
-d '{
"jsonrpc": "2.0",
"id": 1,
"method": "eth_fillTransaction",
"params": [{
"from": "0x0000000000000000000000000000000000000001",
"to": "0x0000000000000000000000000000000000000001",
"value": "0x0",
"type": "0x2"
}]
}'
```

Response:

```json
{
"result": {
"tx": {
"type": "0x2",
"gasPrice": "0x0",
"maxFeePerGas": "0x2e28680",
"maxPriorityFeePerGas": "0x0",
"gas": "0x5f12",
"chainId": "0xa4b1"
}
}
}
```

When a dapp submits a transaction containing these fields to MetaMask, it rejects with:

> Invalid transaction envelope type: specified type "0x2" but included a gasPrice instead of maxFeePerGas and maxPriorityFeePerGas

## Expected Behavior

When a transaction includes both `gasPrice` and `maxFeePerGas`/`maxPriorityFeePerGas` with a fee-market type (`0x2` or `0x4`), MetaMask should gracefully prefer the EIP-1559 fields and strip the redundant `gasPrice`, rather than rejecting the transaction.

## Additional Context

- Originally filed as [wevm/viem#4323](https://github.com/wevm/viem/issues/4323)
- The relevant validation is in `packages/transaction-controller/src/utils/validation.ts`, in `validateGasFeeParams` which calls `ensureMutuallyExclusiveFieldsNotProvided`

Start in packages/transaction-controller/src/utils/validation.ts at validateGasFeeParams and its call to ensureMutuallyExclusiveFieldsNotProvided. Reproduce the provided type 0x2 transaction with both fee styles, then verify that fee-market transactions prefer maxFeePerGas and maxPriorityFeePerGas while legacy transactions retain their existing validation behavior.

Written by the indexing model from the issue text.