fix(vertexai): Update gemini model to gemini-2.5-flash

[alarconesparza]

Description

Fixes Internal:
b/481404468
b/481404611
b/481403956
b/481403794
b/481405008
b/481403799
b/481403720
b/481404947
b/481405007
b/481404786
b/481405042

Checklist

• I have followed Sample Format Guide
• pom.xml parent set to latest shared-configuration
• Appropriate changes to README are included in PR
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• Tests pass: mvn clean verify required
• Lint passes: mvn -P lint checkstyle:check required
• Static Analysis: mvn -P lint clean compile pmd:cpd-check spotbugs:check advisory only
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

[gemini-code-assist]

Summary of Changes

Hello @alarconesparza, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request updates the default Gemini model version across multiple Java code snippets and their corresponding integration tests. The change ensures that the examples leverage the latest gemini-2.5-flash model, providing users with up-to-date and potentially more performant or feature-rich demonstrations. Additionally, it cleans up some outdated or unused test constants.

Highlights

• Model Version Update: The default Gemini model used in various Vertex AI snippets has been updated from gemini-2.0-flash-001 to gemini-2.5-flash.
• Test Snippets Refinement: Several unused constants related to Gemini models, datastore IDs, and translation targets were removed from the SnippetsIT.java test file, streamlining the test configuration.

Changelog

• vertexai/snippets/src/main/java/vertexai/gemini/ControlledGenerationSchema6.java
  • Updated the modelName variable to gemini-2.5-flash.
• vertexai/snippets/src/main/java/vertexai/gemini/FunctionCalling.java
  • Updated the modelName variable to gemini-2.5-flash.
• vertexai/snippets/src/main/java/vertexai/gemini/GetMediaTokenCount.java
  • Updated the modelName variable to gemini-2.5-flash.
• vertexai/snippets/src/main/java/vertexai/gemini/GetTokenCount.java
  • Updated the modelName variable to gemini-2.5-flash.
• vertexai/snippets/src/main/java/vertexai/gemini/Multimodal.java
  • Updated the modelName variable to gemini-2.5-flash.
• vertexai/snippets/src/main/java/vertexai/gemini/QuestionAnswer.java
  • Updated the modelName variable to gemini-2.5-flash.
• vertexai/snippets/src/main/java/vertexai/gemini/Quickstart.java
  • Updated the modelName variable to gemini-2.5-flash.
• vertexai/snippets/src/main/java/vertexai/gemini/StreamingMultimodal.java
  • Updated the modelName variable to gemini-2.5-flash.
• vertexai/snippets/src/main/java/vertexai/gemini/StreamingQuestionAnswer.java
  • Updated the modelName variable to gemini-2.5-flash.
• vertexai/snippets/src/main/java/vertexai/gemini/TextInput.java
  • Updated the modelName variable to gemini-2.5-flash.
• vertexai/snippets/src/main/java/vertexai/gemini/VideoInputWithAudio.java
  • Updated the modelName variable to gemini-2.5-flash.
• vertexai/snippets/src/test/java/vertexai/gemini/SnippetsIT.java
  • Updated the GEMINI_FLASH constant to gemini-2.5-flash.
  • Removed unused constants GEMINI_FLASH_1_5, DATASTORE_ID, TARGET_LANGUAGE_CODE, and TEXT_TO_TRANSLATE.

Activity

• The pull request was created by alarconesparza.
• The author has provided a checklist indicating various checks performed and requested merging upon approval.
• No human comments or reviews have been recorded yet.

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[gemini-code-assist]

Code Review

The pull request successfully updates the Gemini model version to gemini-2.5-flash across various Java snippets. This is a straightforward and necessary update. Additionally, the SnippetsIT.java file has been cleaned up by removing several unused constants (GEMINI_FLASH_1_5, DATASTORE_ID, TARGET_LANGUAGE_CODE, TEXT_TO_TRANSLATE), which is a positive improvement for code maintainability and clarity.

[gemini-code-assist]

While this change correctly updates the model name, for improved maintainability and to avoid 'magic strings', consider defining modelName as a private static final String at the class level. This would centralize the model name definition and make future updates easier, especially since this pattern is repeated across multiple snippet files.