fix(llm): separate retry counters in stream() - transient errors used wrong cap

[Sri-Likhita-adru]

Closes #6105

## Changes
- Add 'STREAM_TRANSIENT_MAX_RETRIES = 3' constant
- Track 'empty_stream_attempts', 'transient_attempts', 'rate_limit_attempts'  as independent counters in 'stream()'
- Each retry branch checks and increments only its own counter
- Transient errors no longer consume the rate-limit retry budget

## Files Changed
'core/framework/llm/litellm.py'

[github-actions]

PR Requirements Warning

This PR does not meet the contribution requirements.
If the issue is not fixed within ~24 hours, it may be automatically closed.

PR Author: @Sri-Likhita-adru
Found issues: #6105 (assignees: none)
Problem: The PR author must be assigned to the linked issue.

To fix:

1. Assign yourself (@Sri-Likhita-adru) to one of the linked issues
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Micro-fix requirements (must meet ALL):

Qualifies	Disqualifies
< 20 lines changed	Any functional bug fix
Typos & Documentation & Linting	Refactoring for "clean code"
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Why is this required? See #472 for details.