Add input validation for field length constraints

[enaboapps]

The SDK doesn't validate field lengths before sending. The ingest API enforces:

• message: 1-10,000 chars
• source: 1-100 chars
• errorName: max 200 chars
• errorStack: max 10,000 chars
• tags: max 20 items, each max 50 chars
• userId, sessionId, requestId: max 100 chars
• version, dataset, flowId: max 50 chars
• stepIndex: 0-1,000

Should validate early and raise clear errors.

Files: timberlogs/types.py, timberlogs/client.py