add proto and compile

src/proto/book.proto

+// book.proto
+syntax = "proto3";
+
+package book;
+
+enum Genre {
+  UNKNOWN = 0;
+  SCIENCE_FICTION = 1;
+  MYSTERY = 2;
+  BIOGRAPHY = 3;
+  HISTORY = 4;
+}
+
+message Author {
+  string first_name = 1;
+  string last_name = 2;
+}
+
+message Book {
+  string title = 1;
+  Author author = 2;
+  string isbn = 3;
+  uint32 publication_year = 4;
+  Genre genre = 5;
+  repeated string tags = 6;
+}
+
+service BookService {
+  rpc GetBook(BookRequest) returns (Book);
+  rpc AddBook(Book) returns (BookResponse);
+}
+
+message BookRequest {
+  string isbn = 1;
+}
+
+message BookResponse {
+  bool success = 1;
+  string message = 2;
+}
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