Calculate GitProvenance only once per build.

In repositories with many commits computing this can be expensive, so avoid any unnecessary repetition of the same computation with caching.

src/main/java/org/openrewrite/maven/MavenMojoProjectParser.java

@@ -767,9 +767,11 @@ private static List<Path> listSources(Path sourceDirectory, String extension) th
         }
     }
 
+    private static final Map<Path, GitProvenance> REPO_ROOT_TO_PROVENANCE = new HashMap<>();
     private @Nullable GitProvenance gitProvenance(Path baseDir, @Nullable BuildEnvironment buildEnvironment) {
         try {
-            return GitProvenance.fromProjectDirectory(baseDir, buildEnvironment);
+            // Computing git provenance can be expensive for repositories with many commits, ensure we do it only once
+            return REPO_ROOT_TO_PROVENANCE.computeIfAbsent(baseDir, dir -> GitProvenance.fromProjectDirectory(dir, buildEnvironment));
         } catch (Exception e) {
             // Logging at a low level as this is unlikely to happen except in non-git projects, where it is expected
             logger.debug("Unable to determine git provenance", e);