refactor(ssj): move MockContractUpgradeable to separate file

[CreeptoGengar]

Time spent on this PR: 0.5 days

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Currently, MockContractUpgradeableV1 is located in test_upgradeable.cairo file, which is no longer needed as mentioned in issue #1559.

Resolves #1559

What is the new behavior?

• Moved MockContractUpgradeableV0 and MockContractUpgradeableV1 contracts to a new file mock_contract_upgradeable.cairo
• Deleted test_upgradeable.cairo as it's no longer needed
• All functionality remains intact and tests are preserved
• Starknet-foundry can still resolve the contract class as it's used in test_kakarot_core.cairo