Copybara import of the project:

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f8a3bdf by Oleksii Oleniuk <58557113+oleksii-oleniuk-star@users.noreply.github.com>:

fix: Add Context Cache support for ChatSessionPreview class (#433)

* add content cache to chat session

* remove logs, add gitignore

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Co-authored-by: Oleksii Oleniuk <oleksii.olenyuk@gmail.com>
Co-authored-by: Yvonne Yu <150068659+yyyu-google@users.noreply.github.com>
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2c92ef3 by Oleksii Oleniuk <oleksii.olenyuk@gmail.com>:

extend UsageMetadata interface

COPYBARA_INTEGRATE_REVIEW=#439 from oleksii-oleniuk-star:feature/gemini-context-cache-4 3ab1693
PiperOrigin-RevId: 686671597

src/types/content.ts

@@ -459,6 +459,8 @@ export declare interface UsageMetadata {
   candidatesTokenCount?: number;
   /** Optional. Total number of tokens. */
   totalTokenCount?: number;
+  /** Optional. Number of tokens in the cached content. */
+  cachedContentTokenCount?: number;
 }
 
 /**