fix: improve model read retry logic for eventual consistency

[shin-bot-litellm]

Summary

Fixes #16 - litellm_model resource intermittently fails with "Root object was present, but now absent" on create

Problem

When creating multiple litellm_model resources in parallel, some randomly fail because:

1. The Create API call succeeds
2. The immediate Read to verify returns empty/nil due to eventual consistency
3. Terraform interprets this as "resource disappeared"

Root Cause

Database eventual consistency - the model is written but not immediately readable, especially under concurrent writes.

Solution

Improved the retry mechanism in retryModelRead():

Before	After
Fixed error string matching	Flexible pattern matching via isRetryableModelError()
No initial delay	200ms initial delay for database sync
1s starting retry delay	500ms starting delay (faster first retry)
5 retries max	8 retries max
~31s max wait	~45s max wait

Error Patterns Now Handled

• "not found" messages
• "Model id = X" patterns
• "model_not_found" sentinel values
• Cleared resource IDs

Retry Timeline

200ms initial delay
500ms → 1s → 2s → 4s → 8s → 10s → 10s → 10s
(exponential backoff with 10s cap)

Testing

The fix addresses the intermittent failure by:

1. Allowing more time for database replication
2. Using robust error detection that won't break with API changes
3. Providing better debug logging