feat: add string functions

src/main.zig

@@ -1,6 +1,10 @@
 const std = @import("std");
 const c = @import("nvim_c");
 
+test {
+    std.testing.refAllDeclsRecursive(@This());
+}
+
 /// Convenient wrapper for nvim's Error
 pub const Error = struct {
     err: c.Error = .{ .type = c.kErrorTypeNone, .msg = null },
@@ -10,6 +14,7 @@ pub const Error = struct {
             c.kErrorTypeNone => {},
             c.kErrorTypeValidation => return error.NvimValidation,
             c.kErrorTypeException => return error.NvimException,
+            else => unreachable,
         }
     }
 
@@ -21,7 +26,22 @@ pub const Error = struct {
         };
     }
 
-    pub fn msg(self: Error) ?[:0]u8 {
+    pub fn msg(self: Error) ?[*:0]u8 {
         return self.err.msg;
     }
 };
+
+pub fn nvimString(data: []u8) c.String {
+    return .{
+        .data = data.ptr,
+        .size = data.len,
+    };
+}
+
+pub fn constNvimString(data: []const u8) c.String {
+    return nvimString(@constCast(data));
+}
+
+pub fn zigString(data: c.String) []u8 {
+    return data.data[0..data.size];
+}