actix-prost: Fail build when selector does not match anything

[bragov4ik]

Description

If selector is written incorrectly and it doesn't match any rpcs, the build just skips generation of actix (server?). This issue becomes non-trivial to debug :)
Instead, it would be useful to fail and report the faulty selector to the user.

Possible solutions

Result of .get there could be used to indicate it:

actix-prost/actix-prost-build/src/generator.rs

Lines 43 to 53 in 32188ff

	service
	.methods
	.iter()
	.filter_map(|m| {
	map.get(&format!(
	"{}.{}.{}",
	service.package, service.proto_name, m.proto_name
	))
	.map(|r| (m, *r))
	})
	.collect()