fix(streaming): handle out-of-order content blocks in accumulation

[Ashutosh0x]

Problem

The SDK's streaming accumulation logic was vulnerable to 'out-of-order' content blocks. Specifically, if the API starts index 1 before index 0 (common when thinking and tools are interspersed), the SDK incorrectly maps these to its internal list, causing data loss or incorrect delta application.

Solution

• Updated accumulate_event in both standard and beta versions to dynamically resize and index the content list based on the index provided by the API.
• This ensures that thinking and tool blocks are correctly maintained in their respective slots, regardless of arrival order.

Verification

• Verified with
  epro_issue_999_thinking_tools.py which covers complex interspersed sequences and explicit out-of-order block initialization.
• Confirmed that standard accumulation and beta accumulation both handle these scenarios correctly.