etc-merge: Refactor and fix dir perms while merging

While merging, existing directory in new_etc was being recursively
deleted which is not correct as any new files might also be deleted.

Instead, we simply create a directory if it doesn't exists, or if it
does exists, we update its metadata accordingly.

Add some test cases for the above.

Signed-off-by: Johan-Liebert1 <pragyanpoudyal41999@gmail.com>

cli: Add internal opt for printing etc-diff

Signed-off-by: Johan-Liebert1 <pragyanpoudyal41999@gmail.com>

etc-merge: Add license to Cargo.toml

Signed-off-by: Johan-Liebert1 <pragyanpoudyal41999@gmail.com>

etc-merge: More refactoring

Signed-off-by: Johan-Liebert1 <pragyanpoudyal41999@gmail.com>

Author: Johan-Liebert1

Cargo.lock

@@ -2,6 +2,8 @@
 name = "etc-merge"
 version = "0.1.0"
 edition = "2024"
+license = "MIT OR Apache-2.0"
+publish = false
 
 [dependencies]
 anyhow = { workspace = true }