chore(l1): rename ef_tests-ethrex crate to ef_tests-blockchain and cleanup

[mpaulucci]

Motivation
We should try to be close to the naming used by the Ethereum foundation, they call these tests "Blockchain tests".

Next step is to rename the other one to "State tests".

See: https://ethereum.github.io/execution-spec-tests/main/consuming_tests/blockchain_test/

Description

• Renamed ef_tests-ethrex to ef_tests-blockchain
• Moved Makefile specific targets to it's own Makefile
• Simplified the Makefile
• From the root Makefile, we can call the ef_tests one with $(MAKE) -C cmd/ef_tests/blockchain test.
• Added README file.

[github-actions]

| File                                                                   | Lines | Diff |
+------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/cmd/ef_tests/blockchain/lib.rs         | 3     | +3   |
+------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/cmd/ef_tests/blockchain/network.rs     | 79    | +79  |
+------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/cmd/ef_tests/blockchain/test_runner.rs | 137   | +137 |
+------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/cmd/ef_tests/blockchain/types.rs       | 384   | +384 |
+------------------------------------------------------------------------+-------+------+

Total lines added: +603
Total lines removed: 0
Total lines changed: 603

[fborello-lambda]

LGTM 🚀