Profile cold unit module loading

docs/wasm-runtime-architecture.md

@@ -137,6 +137,10 @@ own import vector, memory/table-base globals, GOT globals and function-table
 slots, then runs relocations, constructors, and request-pointer binding. This
 removes repeated Wasmtime import-type traversal without sharing request state or
 changing core-first, unit-load-order symbol resolution.
+`request_perf()` reports worker module-cache hits and misses and divides a miss
+into artifact lookup, wasm read, custom-section parse, serialized-module
+deserialization or wasm compilation, and immutable import classification. This
+keeps cold-worker module latency distinguishable without exposing source paths.
 Cold module compilation and deserialization are host work, so `load_unit()`
 refreshes the epoch deadline before its first guest call. Otherwise a component
 whose compilation outlasted the guest CPU budget would immediately trap in the