repo: rename odb -> cache

We used to have it named `cache` before, but these days it is clear that
you can have three odbs: just odb (e.g. in-memory), cache (typically local)
or remote (typically cloud). Fixing naming here before proceeding with
introducing `out.odb` and `out.cache`.

In preparation for migration to https://github.com/iterative/dvc-data/pull/304

tests/unit/data/db/test_local.py

@@ -32,7 +32,7 @@ def test_status_download_optimization(mocker, dvc):
 
 @pytest.mark.parametrize("link_name", ["hardlink", "symlink"])
 def test_is_protected(tmp_dir, dvc, link_name):
-    odb = dvc.odb.local
+    odb = dvc.cache.local
     fs = odb.fs
     link_method = getattr(fs, link_name)
 
@@ -67,7 +67,7 @@ def test_protect_ignore_errors(tmp_dir, dvc, mocker, err):
     tmp_dir.gen("foo", "foo")
 
     mock_chmod = mocker.patch("os.chmod", side_effect=OSError(err, "something"))
-    dvc.odb.local.protect("foo")
+    dvc.cache.local.protect("foo")
     assert mock_chmod.called
 
 
@@ -76,7 +76,7 @@ def test_set_exec_ignore_errors(tmp_dir, dvc, mocker, err):
     tmp_dir.gen("foo", "foo")
 
     mock_chmod = mocker.patch("os.chmod", side_effect=OSError(err, "something"))
-    dvc.odb.local.set_exec("foo")
+    dvc.cache.local.set_exec("foo")
     assert mock_chmod.called
 
 
@@ -88,7 +88,7 @@ def test_staging_file(tmp_dir, dvc):
     tmp_dir.gen("foo", "foo")
     fs = LocalFileSystem()
 
-    local_odb = dvc.odb.local
+    local_odb = dvc.cache.local
     staging_odb, _, obj = build(local_odb, (tmp_dir / "foo").fs_path, fs, "md5")
 
     assert not local_odb.exists(obj.hash_info.value)
@@ -113,7 +113,7 @@ def test_staging_dir(tmp_dir, dvc):
 
     tmp_dir.gen({"dir": {"foo": "foo", "bar": "bar"}})
     fs = LocalFileSystem()
-    local_odb = dvc.odb.local
+    local_odb = dvc.cache.local
 
     staging_odb, _, obj = build(local_odb, (tmp_dir / "dir").fs_path, fs, "md5")