fix: avoid repeated probe summaries

[piotr-iohk]

Summary

• Keep writing partial probe artifacts after each target so diagnostics survive mid-run failures.
• Suppress GitHub step summary writes during partial artifact updates.
• Write the probe step summary only once from the final artifact write.

Context

This regression was introduced by #188, which intentionally started writing probe artifacts after each individual probe result so long-running mainnet probe runs keep partial diagnostics if they fail mid-run.

That change worked for artifact files because probe-results.json and probe-report.md are overwritten on every write. However, writeProbeArtifacts() also appends to GITHUB_STEP_SUMMARY, so every partial write appended the whole growing report again.

The result is visible in this run summary:
https://github.com/synonymdev/bitkit-nightly/actions/runs/28343008353/jobs/67064661419/summary_raw

The uploaded diagnostics artifact still contains a correct final probe-report.md; only the GitHub job summary is repeated/expanded after each probe.

Fix

This keeps the useful #188 behavior for partial artifact files, but disables step-summary writes for those partial updates. The final finally block still writes the GitHub step summary once, after the run has the final result set.

Test plan

• npx eslint test/helpers/probe.ts test/specs/mainnet/probe.e2e.ts
• https://github.com/synonymdev/bitkit-nightly/actions/runs/28355054451