internal/rosa: initial azalea bindings

Supported fields are still rather minimal, but evaluation works, and resulting artifacts cure correctly.

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

internal/rosa/rosa.go

@@ -42,7 +42,7 @@ func mustDecode(s string) pkg.Checksum {
 }
 
 // KV is a key-value pair of strings.
-type KV [2]string
+type KV = [2]string
 
 var (
 	// AbsUsrSrc is the conventional directory to place source code under.
@@ -601,6 +601,9 @@ func newFromGitHubRelease(
 	)
 }
 
+// native contains natively-implemented and built-in azalea-based [Artifact].
+// It is generally recommended to clone this instance for custom [Artifact]
+// registrations.
 var native S
 
 // Native returns the global [S].