Adapt to Starknet 0.12.1

[FabijanC]

Usage related changes

• Adapt to Starknet 0.12.1

Development related changes

• Replace cairo-lang 0.12.1a0 with 0.12.1
• Refactor block loading due to a bug in cairo-lang 0.12.1 which prevents aborted blocks from being loaded via StarknetBlock.load
• Refactor block testing:
  • Expected slight testing speed up since the HTTP call is done directly, not via Starknet CLI - couldn't rely on FeederGatewayClient class because it would do parsing and
  • Remove the parse parameter from get_block util - it was always True except in one case which was refactored

Checklist:

• Applied formatting - ./scripts/format.sh
• No linter errors - ./scripts/lint.sh
• Performed code self-review
• Rebased to the last commit of the target branch (or merged it into my branch)
• Documented the changes
• Linked the issues which this PR resolves
• Updated the tests
• All tests are passing - ./scripts/test.sh

[mikiw]

Looks legit