Implement validate_slacl hook logic

Summary:
Wire up the actual .slacl validation by reusing the existing parse_acl_file parser from restricted_paths_acl_file. The hook now reads file contents for any file named .slacl, attempts to parse it as a valid restricted paths ACL file (TOML format, version 0, REPO_REGION identity type), and rejects the push with a descriptive error on parse failure.

Updates the test assertions from the previous commit to assert Rejected for malformed inputs.

Reviewed By: gustavoavena

Differential Revision: D104667156

fbshipit-source-id: 4bf1136a142281a206fa7f20e7f7a77c98a7cea3

Author: lmvasquezg

eden/mononoke/features/hooks/BUCK

@@ -84,6 +84,7 @@ rust_library(
         "//eden/mononoke/repo_attributes/repo_derived_data:repo_derived_data",
         "//eden/mononoke/repo_attributes/repo_identity:repo_identity",
         "//eden/mononoke/repo_attributes/restricted_paths:restricted_paths",
+        "//eden/mononoke/repo_attributes/restricted_paths_acl_file:restricted_paths_acl_file",
         "//eden/mononoke/scs/if:source_control-rust",
         "//eden/mononoke/scs/if:source_control-rust-clients",
         "//eden/mononoke/servers/slapi/slapi_server/context:context",

eden/mononoke/features/hooks/Cargo.toml

@@ -50,6 +50,7 @@ repo_cross_repo = { version = "0.1.0", path = "../../repo_attributes/repo_cross_
 repo_derived_data = { version = "0.1.0", path = "../../repo_attributes/repo_derived_data" }
 repo_identity = { version = "0.1.0", path = "../../repo_attributes/repo_identity" }
 restricted_paths = { version = "0.1.0", path = "../../repo_attributes/restricted_paths" }
+restricted_paths_acl_file = { version = "0.1.0", path = "../../repo_attributes/restricted_paths_acl_file" }
 sapling-clientinfo = { version = "0.1.0", path = "../../../scm/lib/clientinfo" }
 scuba_ext = { version = "0.1.0", path = "../../common/scuba_ext" }
 serde = { version = "1.0.219", features = ["derive", "rc"] }