Genkit Go v1.3.0

What's Changed

• feat(go/genkit): added background action and model support by @sahdev77 in #3262
• fix(go/ai): fix race condition in concurrent prompt rendering by @eric642 in #3837
• fix(go/plugins/googlegenai): Merge tools instead of replacing when using ai.WithTools() by @marcellmars in #3866
• fix(go): add automatic telemetry metrics for background models by @sahdev77 in #3841
• fix(go/ai): update ModelResponseChunk.Index JSON tag field by @hugoaguirre in #3827
• feat(go/plugin/anthropic): add Anthropic plugin by @hugoaguirre in #3109
• feat(go): add support for code defined schemas by @hugoaguirre in #3490
• feat(go): add support for multi-part tools by @apascal07 in #3897
• feat(go): refactored formatters + added support for formatting streams by @apascal07 in #3905
• fix(go/ai): fixed format resolution + prompt variants metadata by @apascal07 in #3931
• feat(go): added support for durable streaming in flows by @apascal07 in #3961
• feat(go): added DataPrompt and iterator-based stream support by @apascal07 in #3926
• feat(go): added support for embedding prompts into the binary by @apascal07 in #3973
• feat(go/plugins/firebase): added Firestore stream manager by @apascal07 in #4047
• fix(go/plugins/googlegenai): include thoughtSignature in part metadata by @hugoaguirre in #4006

Full Changelog: go/v1.2.0...go/v1.3.0