tests: Add tests for NoopExecutionEngine mock API

[bshastry]

This PR adds test coverage for the mock Engine API interface methods in NoopExecutionEngine across multiple forks (Bellatrix, Deneb, Electra). The tests verify that each fork's implementation maintains its specific interface contract while providing mock behaviors for CL-EL interaction in test scenarios.

The Engine API interface has evolved across forks:

• Bellatrix: Basic interface (notify_new_payload, is_valid_block_hash, get_payload, etc.)
• Deneb: Added parent_beacon_block_root parameter
• Electra: Added execution_requests_list parameter

Add fork-specific test files:

• tests/core/pyspec/eth2spec/test/bellatrix/execution_engine/test_execution_engine_interface.py
• tests/core/pyspec/eth2spec/test/deneb/execution_engine/test_execution_engine_interface.py
• tests/core/pyspec/eth2spec/test/electra/execution_engine/test_execution_engine_interface.py

Improves coverage by 5 SLoC in CL-EL mock implementation, with proper fork-specific interface testing.

[jtraglia]

Hey @bshastry, these are great, thank you!

Could you please move these to the unittests (eg unittests for bellatrix)directory? Like this:

• tests/core/pyspec/eth2spec/test/bellatrix/unittests/test_execution_engine_interface.py

The reason I'm asking for this is because these directories (block_processing, fork, fork_choice, etc) are associated with a test format (see formats) which are exported and run by clients. unittests is the exception here, this directory contains tests which are not exported.

[bshastry]

Hey @bshastry, these are great, thank you!

Could you please move these to the unittests (eg unittests for bellatrix)directory? Like this:

• tests/core/pyspec/eth2spec/test/bellatrix/unittests/test_execution_engine_interface.py

The reason I'm asking for this is because these directories (block_processing, fork, fork_choice, etc) are associated with a test format (see formats) which are exported and run by clients. unittests is the exception here, this directory contains tests which are not exported.

Thank you for your review! I have moved the tests to the respective forks' unittests directory. 🙏

[jtraglia]

LGTM, thanks!