Rename and move RandomTest into test-sol/ directory

[arthurgousset]

Scope

Rename RandomTest to RandomMock, and move the file to a new folder mocks/ in protocol/test-sol/unit/identity.

Context

From Slack:

Quick question: Any reason these two contracts should continue to exist as standalone contracts?
protocol/contracts/identity/test/ > RandomTest.sol. Are we keeping Random.sol on the L2?
protocol/contracts/common/libraries/test/ > BLS12Passthrough.sol. Are we keeping B12.sol on the L2?
I'm asking because RandomTest.sol and BLS12Passthrough.sol are the only smart contract tests that fail on forge test.
We can simply exclude them globally when running forge test, but I realised that I don't know if they are an artifact of the past or really in still use.
cc @blockchain-team (I believe RandomTest.sol is tested in the Cel1 geth client according to this PR: Add solidity wrappers for CIP-20/30/31 precompiles#10240)

random is no longer on L2. it was used by ASV1, which is deprecated.

Yes. We deprecated random. It’s on the specs docs

[arthurgousset]

Looks like it's used here:

celo-monorepo/packages/protocol/test-sol/unit/identity/Random.t.sol

Line 14 in fec2623

RandomTest random;