internal/rosa: expose in-place behaviour in generic helper

This change also combines the createDir and wantsDir methods, and replaces the non-inplace target of the generic helper with a deterministic path.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/package/unzip.az

@@ -15,10 +15,12 @@ package unzip {
 		compress = gzip;
 	};
 
+	enterSource = true;
 	writable = true;
 	chmod = true;
 
 	exec = generic {
+		inPlace = true;
 		build = `unix/configure
 make -f unix/Makefile generic1`;
 		install = `