Added a auto-refresh of token after rate limit sleep

[mwnickerson]

Summary

• Adds automatic refresh of GitHub App installation tokens after extended sleeps (e.g., rate‑limit backoffs or OS sleep) to prevent using expired credentials.
• Keeps PAT sessions unchanged; only GitHub App sessions refresh.

What Changed

• New Invoke-OptionalTokenRefresh helper to refresh when available without hard dependency.
• New Update-GitHubSessionToken to renew installation tokens when expired or expiring within 5 minutes.
• New Get-GitHubAppInstallationToken to fetch a fresh token using the app’s JWT.
• New-GitHubJwtSession now persists AppCredentials and TokenExpiry on the session for later refreshes.
• Wait-GithubRateLimitReached now calls Invoke-OptionalTokenRefresh after sleeping.

Why

• Long sleeps (rate limits or machine sleep) often outlive installation token TTL, causing subsequent calls to fail with 401/403.
• Proactively refreshing prevents mid-run failures and reduces manual intervention.

How It Works

• For sessions created via New-GitHubJwtSession, we store ClientId, PrivateKeyPath, AppId, and TokenExpiry.
• After a long sleep (rate limit), Invoke-OptionalTokenRefresh runs; if the token is expired or within 5 minutes of expiry, a new token is fetched and headers are updated.
• No-ops for PAT sessions (no AppCredentials on the session).

Backward Compatibility

• PAT flows unchanged.
• GitHub App flows improve resilience; no breaking API surface changes.

Testing

• App session: run a request, simulate a long sleep beyond token TTL, verify automatic refresh and continued success.
• Near-expiry: set TokenExpiry to <5 minutes from now and verify refresh triggers.
• PAT session: verify no refresh call is attempted and behavior remains the same.
• Rate limit: force rate-limit sleep and confirm refresh occurs post-sleep when appropriate.