feat(parser): support Docker and OpenTelemetry JSON fields

[vinnytherobot]

Summary

• Extend JSON log parsing to support Docker log payloads.
• Add OpenTelemetry-style severity/message fields via severity_text, severityText, and body.
• Extract service metadata from resource.attributes.service.name.
• Infer severity from embedded bracket-style Docker log messages when no explicit JSON severity is present.
• Document supported JSON fields in README and API reference.

Technical Notes

The parser now centralizes common JSON field lookup through helper constants and helpers, preserving the existing bracket-log and legacy JSON behavior. Docker log payloads have trailing line endings trimmed before nested parsing, allowing [ERROR] message payloads to produce the canonical ERROR level and cleaned message.

Validation

• pytest -q
• ruff check .
• pytest --cov=logscope --cov-report=term-missing
• python -m build

[github-actions]

PR Check Summary

• Conventional title: feat(parser): support Docker and OpenTelemetry JSON fields
• Tests updated when code changes: true
• Docs updated when code changes: true