feat: add store abstractions

* feat/store:
  refactor: rename modules, fix panics, configurable identity/message in git-store
  fix: reject empty paths in `Tx` operations
  feat: implement Store and Tx for phase 1 transaction

Author: jdc-pub

crates/git-store/Cargo.toml

@@ -6,7 +6,7 @@ publish.workspace = true
 license.workspace = true
 
 [dependencies]
-gix = { workspace = true }
+gix = { workspace = true, features = ["tree-editor"] }
 thiserror = { workspace = true }
 
 [dev-dependencies]