refactor: foundation cleanup - rename, edition fixes, constants, coverage CI

[flyq]

Summary

Foundation cleanup that renames the core crate, fixes workspace consistency issues, deduplicates constants, and adds coverage CI infrastructure.

Changes

• Rename validator-core → stateless-core: renamed the crate directory, updated Cargo.toml, all use validator_core:: references across the workspace, docs (README.md, AGENTS.md), CODEOWNERS, and logging filter directives.
• Fix debug-trace-server workspace fields: set edition.workspace = true and version.workspace = true (was hardcoded to 2021 / 0.1.0).
• Deduplicate constants: move DEFAULT_METRICS_PORT to stateless-common and re-export from both binaries; remove duplicate SLOW_STAGE_THRESHOLD_MS declaration (was in both data_provider.rs and rpc_service.rs).
• Add coverage CI: add scripts/coverage_stateless_core.sh and .github/workflows/coverage.yml for coverage reporting via cargo-llvm-cov + Codecov (following mega-evm pattern), plus .github/codecov.yml config targeting the stateless-core package.

Files changed

38 files changed across the workspace (283 insertions, 152 deletions), including the full directory rename from crates/validator-core/ to crates/stateless-core/.

[claude]

The rename is complete and consistent across all 38 files — Cargo manifests, imports, docs, CODEOWNERS, logging filters, and the lock file. Workspace field inheritance for debug-trace-server and constant deduplication (DEFAULT_METRICS_PORT, SLOW_STAGE_THRESHOLD_MS) are done cleanly.

Coverage CI looks standard: --locked, proper artifact upload, Codecov path fix is the expected pattern for the GitHub Actions runner path.

One stale comment flagged inline. Nothing else to address.

[claude]

Clean, mechanical rename — the codebase changes are consistent and complete. One minor issue flagged inline.

Coverage CI

• fail_ci_if_error: false on the Codecov upload step means a missing/expired CODECOV_TOKEN secret will fail silently. Consider flipping this to true once the token is confirmed to be configured, so breakage is visible.
• The fixes path in codecov.yml is correct for the GitHub Actions runner environment and follows the established pattern.

Everything else (constant deduplication, workspace field alignment, let-chain refactoring in tests) looks good.

[claude]

The rename is clean and complete — all references updated consistently across workspace, docs, CODEOWNERS, and logging directives. Workspace field fixes and constant deduplication are good. Two minor issues in the coverage setup worth addressing.

[claude]

The rename is clean and consistent across the workspace. A few notes:

Behavioral changes not called out in the description

bin/stateless-validator/src/main.rs has two silent behavior changes:

• Shutdown timeout bumped 1s → 3s.
• JoinError handling split: cancelled tasks now log at debug (was warn), unexpected terminations at error (was warn). Both are improvements — worth mentioning in the summary so reviewers don't overlook them.

Previous review threads

Both open threads are addressed by this revision:

• The coverage script uses --no-default-features (not --all-features), which is correct — the only feature is test-bucket-resize, which alters SALT bucket sizing and shouldn't be included.
• No Foundry install step in the coverage workflow.

Resolved both threads.