UserCache: env var to enable agressive cache writing

When using oca-port as a Python package to collect migration data where
repositories are cloned on a filesystem with very low IO perf, the
process could take a lot of time to finish (every underlying git operations
to retrieve for instance updated file paths of a commit are very
costly). Such process could be killed before it actually finishes (and
write the data in cache).

By setting the OCA_PORT_AGRESSIVE_CACHE_WRITE environment variable, we
force oca-port to update the cache very often, generating more IO during
the first analysis of a module, but making the next process execution
much faster.

As this is an advanced option, it is exposed through an environment
variable to not clutter the usual parameters.

oca_port/utils/cache.py

@@ -221,13 +221,25 @@ def set_commit_files(self, commit_sha: str, files: list):
         if self.readonly:
             return
         self._commits_data[commit_sha]["files"] = list(files)
+        if os.environ.get("OCA_PORT_AGRESSIVE_CACHE_WRITE"):
+            # IO can be very slow on some filesystems (like checking modified
+            # paths of a commit), and saving the cache on each analyzed commit
+            # could help in case current oca-port process is killed before
+            # writing its cache on disk, so the next call will be faster.
+            self._save_commits_data()
 
     def save(self):
         """Save cache files."""
         if self.readonly:
             return
+        self._save_commits_to_port()
+        self._save_commits_data()
+
+    def _save_commits_to_port(self):
         # commits/PRs to port
         self._save_cache(self._commits_to_port, self._commits_to_port_path)
+
+    def _save_commits_data(self):
         # commits data file
         self._save_cache(self._commits_data, self._commits_data_path)