docs: Update package names from ethereum_test_* to execution_testing.*

[aryanpatil2703]

🗒️ Description

Update documentation to reflect package renaming from ethereum_test_* to execution_testing.* namespace (follow-up to PR #1654).

Changes:

• Update module references in eip_testing_checklist_template.md
• Update directory structure in repository_overview.md

All module references now use the unified execution_testing.* namespace.

🔗 Related Issues or PRs

Fixes #1672

✅ Checklist

• All: Ran fast tox checks to avoid unnecessary CI fails

  • Note: Changes are documentation-only (markdown files) and have been manually verified.

• All: PR title adheres to the repo standard - starts with type(scope):

  • Commit message: docs: update package names from ethereum_test_* to execution_testing.*

• All: Considered adding an entry to CHANGELOG.md

  • Not needed: This is a documentation-only change following up on PR refactor(testing): improve layout and naming of testing packages #1654

• All: Considered updating the online docs

  • Updated: docs/getting_started/repository_overview.md and docs/writing_tests/checklist_templates/eip_testing_checklist_template.md

• All: Set appropriate labels for the changes (only maintainers can apply labels).

• Tests: Not applicable - No new tests added

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