Separate preparation timeouts for PVF prechecking and execution (#6139)

* Add some documentation

* Add `compilation_timeout` parameter for PVF preparation job

* Update buckets in prometheus metrics

* Update prepare/queue tests

* Update pvf-prechecking overview in implementer docs

* Fix some CI checks

polkadot/node/core/pvf/src/metrics.rs

@@ -155,7 +155,8 @@ impl metrics::Metrics for Metrics {
 						"Time spent in preparing PVF artifacts in seconds",
 					)
 					.buckets(vec![
-						// This is synchronized with COMPILATION_TIMEOUT=60s constant found in
+						// This is synchronized with the PRECHECK_COMPILATION_TIMEOUT=60s
+						// and EXECUTE_COMPILATION_TIMEOUT=180s constants found in
 						// src/prepare/worker.rs
 						0.1,
 						0.5,
@@ -166,6 +167,7 @@ impl metrics::Metrics for Metrics {
 						20.0,
 						30.0,
 						60.0,
+						180.0,
 					]),
 				)?,
 				registry,