Create a more rigid overseer builder pattern that fails at compile time (#4753)

Introduces `Missing<Field>` and `Init<Field>` states, that are used in place of builder generics, and make this possible.

polkadot/node/service/src/overseer.rs

@@ -30,8 +30,8 @@ pub use polkadot_overseer::{
 	HeadSupportsParachains,
 };
 use polkadot_overseer::{
-	metrics::Metrics as OverseerMetrics, BlockInfo, MetricsTrait, Overseer, OverseerBuilder,
-	OverseerConnector, OverseerHandle,
+	metrics::Metrics as OverseerMetrics, BlockInfo, InitializedOverseerBuilder, MetricsTrait,
+	Overseer, OverseerConnector, OverseerHandle,
 };
 
 use polkadot_primitives::v2::ParachainHost;
@@ -142,7 +142,7 @@ pub fn prepared_overseer_builder<'a, Spawner, RuntimeClient>(
 		pvf_checker_enabled,
 	}: OverseerGenArgs<'a, Spawner, RuntimeClient>,
 ) -> Result<
-	OverseerBuilder<
+	InitializedOverseerBuilder<
 		Spawner,
 		Arc<RuntimeClient>,
 		CandidateValidationSubsystem,