Gemma4 tool calling grammar (#344)

* Add Gemma4 tool prompt context extraction

* Add Gemma4 VLM reasoning guard

* Optimize Gemma4 reasoning guard token tracking

* Simplify Gemma4 reasoning guard state

* Document Gemma4 reasoning mask tradeoff

* Simplify Gemma4 token helper assumptions

* Optimize Gemma4 guard no-mask path

* Avoid Gemma4 guard token sync

* Simplify Gemma4 reasoning guard markers

* Add Gemma4 tool-call structure guard

* Use llguidance for Gemma4 tool grammar

* Simplify Gemma4 llguidance guard

* Move llguidance imports to module scope

* Simplify Gemma4 tool runtime assumptions

* Relax Gemma4 tool grammar edge cases

* Trim Gemma4 tool runtime comments

* Rename Gemma4 grammar edge case test

* Document Gemma4 tool processor flow

* Rename Gemma4 token boost helper

* Inline Gemma4 tool processor helpers

* Clarify Gemma4 tool-call bridge

* Preserve Gemma4 post-tool continuation scores

* Support namespaced Gemma4 tool names