Pytest sync test

[OlufemiAdeOlusile]

Summary

This PR migrates the sync-test flow toward direct pytest-based GitHub Actions execution on self-hosted NixOS runners, replacing the old script-heavy / Buildkite-oriented path for node and db-sync validation.

Key Changes

• Added GitHub Actions workflows for node sync and full db-sync runs, including inputs for environment, node/db-sync revisions, db-sync start options, cleanup, and artifact upload.
• Introduced pytest session fixtures for node sync, db-sync setup, Postgres lifecycle, marker writing, and artifact generation.
• Added phase-aware CI heartbeats so long sync runs show periodic status without flooding the Actions log.
• Split CI logs into focused files:
  • ci_step.log for nix develop, shell setup, and pytest output.
  • nix_build.log for execute_command() Nix build output.
  • node_sync.log and db_sync.log for process logs.
• Reduced Actions log noise by lowering routine progress logs, quieting pip in CI, and printing a concise pytest summary at the end.
• Improved artifact bundling by separating monitor/OOM/Postgres logs into monitor.zip while keeping sync logs/results in their own bundles.
• Added tests for CI log capture, artifact generation, and disk cleanup behavior.
• Fixed low-risk cleanup issues:
  • Guarded db-sync epoch export process cleanup.
  • Used captured node base directory during teardown.
  • Closed matplotlib figures after chart generation.
  • Normalized failed-sync logging format.

Test Plan

• Ran focused pytest checks for disk cleanup and CI log capture.
• Verified node/db-sync artifact tests collect successfully.
• Ran Ruff checks/formatting on affected Python files.
• Manually validated GitHub Actions heartbeat/log behavior through workflow runs.