Optimize some iterations in BodyExtractor and BodyInserter

This commit turns some stream-based iterations back into simpler
enhanced for loops.

For simple use cases like these, where the stream API is merely used to
map/filter + collect to a List, a for loop is more efficient.
This is especially true for small collections like the ones we deal
with in BodyInserters/BodyExtractors here (in the order of 50ns/op vs
5ns/op). These cases are also simple enough that they don't lose in
readability after the conversion.

Closes gh-30136

spring-web/src/main/java/org/springframework/http/client/reactive/AbstractClientHttpRequest.java

@@ -147,8 +147,10 @@ public abstract class AbstractClientHttpRequest implements ClientHttpRequest {
 			this.commitActions.add(writeAction);
 		}
 
-		List<? extends Publisher<Void>> actions = this.commitActions.stream()
-				.map(Supplier::get).toList();
+		List<Publisher<Void>> actions = new ArrayList<>(this.commitActions.size());
+		for (Supplier<? extends Publisher<Void>> commitAction : this.commitActions) {
+			actions.add(commitAction.get());
+		}
 
 		return Flux.concat(actions).then();
 	}