fix(rust): remove unused imports, variables, and dead code causing CI build failures

- Remove unused imports: AtomicBool, Future (provider.rs), debug (executor.rs)
- Remove unused import WorkflowScript (workflow.rs)
- Remove unused variables: tool_name, t_ctx, t_args (executor.rs)
- Remove dead variable class_indent (semantic_search.rs)

CI was failing with 'error: could not compile zesdex-infrastructure
due to 10 previous errors' caused by -D warnings treating unused
code as compilation errors.

apps/infrastructure/src/llm/provider.rs

@@ -2,9 +2,7 @@
 //! supporting both non-streaming and SSE-streaming requests with automatic retry.
 
 use rand_core::RngCore;
-use std::sync::atomic::AtomicBool;
 use std::time::Duration;
-use std::future::Future;
 
 use zesdex_domain::core::{
     ChatMessage, ChatRequest, ChatResponse, SseParser, StreamEvent, StreamOptions, ToolDef,