Implement version control and change log for problem files (#47)

* feat: implement version control and change log for problem files using git2

* refactor: Remove accepted, rejected subdirectory in solution

* fix: cargo fmt

* fix: Set git repository config

* fix: Update error message and comments

* refactor: extract default directory names to a constant array

* refactor: simplify get_repository error handling using and_then and with_context

* refactor: Move git user config setup from get_repository to git_init

Author: reddevilmidzy

Cargo.toml

@@ -14,11 +14,12 @@ name = "coduck-backend"
 anyhow = "1.0"
 axum = { version = "0.8.4", features = ["json", "multipart"] }
 chrono = { version = "0.4.38", features = ["serde"] }
-reqwest = { version = "0.12.19", features = ["json", "rustls-tls"] }
+git2 = "0.20.2"
 serde = { version = "1.0.219", features = ["derive"] }
 serde_json = "1.0.133"
 tokio = { version = "1.45.1", features = ["full"] }
 uuid = { version = "1.17.0", features = ["v4"] }
 
 [dev-dependencies]
+reqwest = { version = "0.12.19", features = ["json", "rustls-tls"] }
 rstest = "0.25.0"