legacy: move LegacyRepository, LegacyRemoteRepository, RepoObj1 into borg.legacy package, refs #9556

Create borg.legacy subpackage to isolate Borg 1.x code from the 2.x codebase.

- Add src/borg/legacy/__init__.py
- Move LegacyRepository + LoggedIO to borg.legacy.repository
- Move LegacyRemoteRepository to borg.legacy.remote
- Move RepoObj1 to borg.legacy.repoobj
- Replace original files with backward-compatible re-export stubs
- Update all consumer imports to use borg.legacy.* paths directly

Author: mr-raj12

src/borg/archiver/_common.py

@@ -13,11 +13,12 @@
 from ..helpers.nanorst import rst_to_terminal
 from ..manifest import Manifest, AI_HUMAN_SORT_KEYS
 from ..patterns import PatternMatcher
-from ..legacyremote import LegacyRemoteRepository
+from ..legacy.remote import LegacyRemoteRepository
 from ..remote import RemoteRepository
-from ..legacyrepository import LegacyRepository
+from ..legacy.repository import LegacyRepository
 from ..repository import Repository
-from ..repoobj import RepoObj, RepoObj1
+from ..repoobj import RepoObj
+from ..legacy.repoobj import RepoObj1
 from ..patterns import (
     ArgparsePatternAction,
     ArgparseExcludeFileAction,

src/borg/archiver/transfer_cmd.py

@@ -10,7 +10,7 @@
 from ..helpers.argparsing import ArgumentParser, ArgumentTypeError
 from ..item import ChunkListEntry
 from ..manifest import Manifest
-from ..legacyrepository import LegacyRepository
+from ..legacy.repository import LegacyRepository
 from ..repository import Repository
 
 from ..logger import create_logger

src/borg/helpers/parseformat.py

@@ -1335,9 +1335,9 @@ def ellipsis_truncate(msg, space):
 
 class BorgJsonEncoder(json.JSONEncoder):
     def default(self, o):
-        from ..legacyrepository import LegacyRepository
+        from ..legacy.repository import LegacyRepository
         from ..repository import Repository
-        from ..legacyremote import LegacyRemoteRepository
+        from ..legacy.remote import LegacyRemoteRepository
         from ..remote import RemoteRepository
         from ..archive import Archive
         from ..cache import AdHocWithFilesCache

src/borg/legacy/__init__.py

@@ -0,0 +1,8 @@
+"""
+Borg Legacy Package — Borg 1.x compatibility layer.
+
+This package contains all code specific to reading/writing Borg 1.x repositories.
+It is required for ``borg transfer --from-borg1`` and ``borg serve`` (serving v1 clients).
+
+This package can be removed entirely when Borg 1.x support is dropped.
+"""