feat(core): implement Git repository operations with gRPC services

- Add advertise_refs functionality for Git protocol communication
- Implement archive service with TAR/ZIP format support and streaming
- Create blame service for Git file annotation with line tracking
- Add branch management including create, delete, rename and compare operations
- Implement merge checking with conflict detection and fast-forward handling
- Add cherry-pick functionality for applying commits between branches
- Integrate gix library for Git repository operations and object handling
- Add comprehensive test suite covering all Git operations
- Implement proper error handling and repository validation
- Add pagination support for large result sets
- Create protobuf definitions for all Git operations and data structures
- Add build system for gRPC code generation and dependency management

oid.rs

@@ -0,0 +1,53 @@
+use serde::{Deserialize, Serialize};
+
+/// The null OID representing "no object" in git protocol.
+pub const ZERO_OID: &str = "0000000000000000000000000000000000000000";
+
+#[derive(Deserialize, Serialize, Clone, Debug, PartialEq, Eq)]
+pub struct ObjectId(pub String);
+
+impl ObjectId {
+    pub fn new(hex: impl AsRef<str>) -> Self {
+        Self(hex.as_ref().to_lowercase())
+    }
+    pub fn as_str(&self) -> &str {
+        &self.0
+    }
+}
+impl std::fmt::Display for ObjectId {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+impl AsRef<str> for ObjectId {
+    fn as_ref(&self) -> &str {
+        &self.0
+    }
+}
+
+pub fn hex_to_bytes(hex: &str) -> Result<Vec<u8>, crate::error::GitError> {
+    let hex = hex.trim();
+    if !hex.len().is_multiple_of(2) {
+        return Err(crate::error::GitError::InvalidOid(
+            "hex oid has odd length".into(),
+        ));
+    }
+
+    (0..hex.len())
+        .step_by(2)
+        .map(|idx| {
+            u8::from_str_radix(&hex[idx..idx + 2], 16)
+                .map_err(|e| crate::error::GitError::InvalidOid(e.to_string()))
+        })
+        .collect()
+}
+
+impl TryFrom<&ObjectId> for gix::hash::ObjectId {
+    type Error = crate::error::GitError;
+
+    fn try_from(id: &ObjectId) -> Result<Self, Self::Error> {
+        gix::hash::ObjectId::from_hex(id.as_str().as_bytes())
+            .map_err(|e| crate::error::GitError::InvalidOid(format!("invalid hex oid: {e}")))
+    }
+}