Remove ethers dependency from the utils package

[danielbate]

Since our move to Vitest in #1310, although the API is very close to Jest, there are differences in how Jest approaches mocking. One area is that we can no longer mock dependencies that are used by test setup files. Such as our dependency on ethers to hexlify a test worker ID to retrieve a private key, to access a faucet to be used in tests.

We now see the following error - source:

Error: [vitest] Cannot mock "ethers" because it is already loaded. Did you import it in a setup file?

Since we have introduced our own hexlify function in #1401, we can use this instead. However we will then need to remove the ethers dependency from the utils package. The main awkwardness for this is the BytesLike type that is used across the SDK. However we should look to introduce our own to across the board reduce our dependency on ethers.

We have also pinned our vitest version to counteract this error, so currently we risk being out of date.

[nedsalk]

@danielbate While you're at it, you can look into removing it totally based on #1592.

[arboleya]

Completed via #1640