fix: code quality improvements across C codebase

- Replace sprintf with snprintf (1024-byte errbuf) in hmmmm.c, base_device.c,
  compose_device.c, config.c
- Fix WRITE_MEM macro: use smartAddrWriteHandlers for write ident (was
  incorrectly reading from smartAddrReadHandlers)
- Replace alloca with malloc+free in dispatchMemAccessNotifications
- Guard closeBaseDevice against NULL lib/partial initialization
- Simplify intercept context storage to single contiguous allocation
- Add NULL checks after calloc in config handler with proper cleanup
- Guard find_device_by_id against zero-length path

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

inc/context.h

@@ -32,7 +32,7 @@ typedef struct {
     uint8_t** devicesMem;
     size_t devicesCount;
     void** deviceHandles;   // device_handle_t** — dynamically loaded devices
-    void** interceptCtxs;   // intercept_ctx_t** — heap-allocated intercept contexts
+    void* interceptCtxs;    // contiguous intercept_ctx_t array (freed as single block)
     size_t interceptCtxCount;
     flatcc_builder_t stream_builder;
 } EmulContext;