fix(v4-sdk): loosen v4 last pool check invariant (#288)

## PR Scope

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## Description

_[Summary of the change, motivation, and context]_

## How Has This Been Tested?

_[e.g. Manually, E2E tests, unit tests, Storybook]_

## Are there any breaking changes?

_[e.g. Type definitions, API definitions]_

If there are breaking changes, please ensure you bump the major version Bump the major version (by using the title `feat(breaking): ...`), post a notice in #eng-sdks, and explicitly notify all Uniswap Labs consumers of the SDK.

## (Optional) Feedback Focus

_[Specific parts of this PR you'd like feedback on, or that reviewers should pay closer attention to]_

## (Optional) Follow Ups

_[Things that weren't addressed in this PR, ways you plan to build on this work, or other ways this work could be extended]_

sdks/v4-sdk/src/entities/pool.test.ts

@@ -1,4 +1,4 @@
-import { Token, CurrencyAmount, WETH9 } from '@uniswap/sdk-core'
+import { Token, CurrencyAmount, WETH9, Ether, ChainId } from '@uniswap/sdk-core'
 import { Pool, DYNAMIC_FEE_FLAG } from './pool'
 import JSBI from 'jsbi'
 import { nearestUsableTick, encodeSqrtRatioX96, TickMath } from '@uniswap/v3-sdk'
@@ -261,6 +261,38 @@ describe('Pool', () => {
     expect(pool.involvesCurrency(WETH9[1])).toEqual(false)
   })
 
+  describe('#v4InvolvesToken', () => {
+    const pool = new Pool(
+      Ether.onChain(ChainId.MAINNET),
+      DAI,
+      FEE_AMOUNT_LOW,
+      TICK_SPACING_TEN,
+      ADDRESS_ZERO,
+      encodeSqrtRatioX96(1, 1),
+      0,
+      0,
+      []
+    )
+    expect(pool.v4InvolvesToken(Ether.onChain(ChainId.MAINNET))).toEqual(true)
+    expect(pool.v4InvolvesToken(DAI)).toEqual(true)
+    expect(pool.v4InvolvesToken(WETH9[1])).toEqual(true)
+
+    const pool2 = new Pool(
+      Ether.onChain(ChainId.MAINNET).wrapped,
+      DAI,
+      FEE_AMOUNT_LOW,
+      TICK_SPACING_TEN,
+      ADDRESS_ZERO,
+      encodeSqrtRatioX96(1, 1),
+      0,
+      0,
+      []
+    )
+    expect(pool2.v4InvolvesToken(Ether.onChain(ChainId.MAINNET))).toEqual(true)
+    expect(pool2.v4InvolvesToken(DAI)).toEqual(true)
+    expect(pool2.v4InvolvesToken(WETH9[1])).toEqual(true)
+  })
+
   describe('swaps', () => {
     let pool: Pool
     let poolWithSwapHook: Pool

sdks/v4-sdk/src/entities/pool.ts

@@ -160,6 +160,20 @@ export class Pool {
     return this.involvesCurrency(currency)
   }
 
+  /**
+   * v4-only involvesToken convenience method, used for mixed route ETH <-> WETH connection only
+   * @param currency
+   */
+  public v4InvolvesToken(currency: Currency): boolean {
+    return (
+      this.involvesCurrency(currency) ||
+      currency.wrapped.equals(this.currency0) ||
+      currency.wrapped.equals(this.currency1) ||
+      currency.wrapped.equals(this.currency0.wrapped) ||
+      currency.wrapped.equals(this.currency1.wrapped)
+    )
+  }
+
   /**
    * Returns the current mid price of the pool in terms of currency0, i.e. the ratio of currency1 over currency0
    */