v2.8.0

v2.8.0: Comprehensive OpenTelemetry tracing coverage

- Add detailed span tracing to all sources (MySQL, PostgreSQL, Folder, LVM, Azure, SFTP)
- Add detailed span tracing to all destinations (S3, GDrive, Minio, B2, Dropbox)
- Include metadata attributes: DB hosts/names, file paths, buckets, GPG recipients, timing, errors
- Cloudflare Backup Registry notification includes trace_id and gpg_recipients
- Add _get_tracer() fallback to all source/destination classes for graceful degradation
- Update README and docs with tracing details
- Bump version to 2.8.0