Python: added cache_write_tokens as required field

[subhrm]

Motivation & Context

openai added cache_write_tokens as a required field on InputTokensDetails. agent-framework-devui 1.0.0b260709 predates this change and constructs InputTokensDetails(cached_tokens=0) at three call sites in _mapper.py, omitting the now-required field. This causes a Pydantic ValidationError on every agent invocation, making the devui completely non-functional with current anthropic versions.

Description & Review Guide

Patched three call sites in agent_framework_devui/_mapper.py to pass cache_write_tokens=0 alongside the existing cached_tokens=0:

• Line 402 — success path usage accumulator
• Line 415 — fallback/estimated usage path
• Line 1872 — error response path

No logic changes — purely adding the missing required field with a zero value to satisfy the updated Pydantic model contract.

Related Issue

Fixes #7048

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after any language prefix) — a workflow keeps the label and title prefix in sync automatically.

[Copilot]

Pull request overview

Fixes a compatibility break in the DevUI response mapper where constructing InputTokensDetails without the now-required cache_write_tokens field causes a Pydantic ValidationError, preventing any agent invocation from completing.

Changes:

• Add cache_write_tokens=0 to InputTokensDetails(...) construction in the successful usage path.
• Add cache_write_tokens=0 to InputTokensDetails(...) construction in the fallback/estimated usage path.
• Add cache_write_tokens=0 to InputTokensDetails(...) construction in the error response path.

[moonbox3]

Could we add test coverage for the accumulated-usage, fallback, and error-response paths?