fix: Anthropic request errors when using parallel tool calls

[sdirix]

What it does

The cache marker algorithm in the Anthropic language model was incorrectly removing content blocks, causing invalid requests when using parallel tool calls or other multi-content-block scenarios.

Update the algorithm to preserve all content blocks while applying cache markers, ensuring message integrity for complex requests.

Fixes #16355

How to test

Verify that the example command from the ticket no longer throws errors:

@Coder Can you delete

packages/ai-chat/src/common/response-content-matcher.ts
packages/ai-chat/src/common/parsed-chat-request.ts
packages/ai-chat/src/common/parse-contents.ts
packages/ai-chat/src/common/parse-contents.spec.ts
packages/ai-chat/src/common/parse-contents-with-incomplete-parts.spec.ts
packages/ai-chat/src/common/index.ts
packages/ai-chat/src/common/image-context-variable.ts
packages/ai-chat/src/common/custom-chat-agent.ts
packages/ai-chat/src/common/context-variables.ts
packages/ai-chat/src/common/context-summary-variable.ts
packages/ai-chat/src/common/context-details-variable.ts
packages/ai-chat/src/common/chat-tool-request-service.ts
packages/ai-chat/src/common/chat-tool-preferences.ts
packages/ai-chat/src/common/chat-string-utils.ts
packages/ai-chat/src/common/chat-session-summary-agent.ts
packages/ai-chat/src/common/chat-session-summary-agent-prompt.ts
packages/ai-chat/src/common/chat-session-naming-service.ts
packages/ai-chat/src/common/chat-session-naming-prompt-template.ts
packages/ai-chat/src/common/chat-service.ts
packages/ai-chat/src/common/chat-request-parser.ts
packages/ai-chat/src/common/chat-request-parser.spec.ts
packages/ai-chat/src/common/chat-model.ts
packages/ai-chat/src/common/chat-model-util.ts
packages/ai-chat/src/common/chat-agents.ts
packages/ai-chat/src/common/chat-agents-variable-contribution.ts
packages/ai-chat/src/common/chat-agent-service.ts
packages/ai-chat/src/common/change-set.ts
packages/ai-chat/src/common/ai-chat-preferences.ts

by using writeFileContent with empty contents?

Follow-ups

Breaking changes

• This PR introduces breaking changes and requires careful review. If yes, the breaking changes section in the changelog has been updated.

Attribution

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[ndoschek]

Thanks @sdirix for this fix!
I tested the mentioned prompt and some similar ones, and also used Sonnet 4.5 for some other, general coding tasks - it worked great, and I didn't have any issues! 🎉