[server] share one reader API across whole context

I don't see why we would have to recreate this for every module because it only depends on com and cc, and carries no additional state.

src/compiler/server.ml

@@ -564,7 +564,14 @@ and type_module sctx com mpath p =
 			begin match check_module sctx mpath mc.mc_extra p with
 				| None ->
 					let reader = new HxbReader.hxb_reader mpath com.hxb_reader_stats in
-					let api = (new hxb_reader_api_server com cc :> HxbReaderApi.hxb_reader_api) in
+					let api = match com.hxb_reader_api with
+						| Some api ->
+							api
+						| None ->
+							let api = (new hxb_reader_api_server com cc :> HxbReaderApi.hxb_reader_api) in
+							com.hxb_reader_api <- Some api;
+							api
+					in
 					let f_next chunks until =
 						let t_hxb = Timer.timer ["server";"module cache";"hxb read"] in
 						let r = reader#read_chunks_until api chunks until in

src/context/common.ml

@@ -419,6 +419,7 @@ type context = {
 	(* misc *)
 	mutable basic : basic_types;
 	memory_marker : float array;
+	mutable hxb_reader_api : HxbReaderApi.hxb_reader_api option;
 	hxb_reader_stats : HxbReader.hxb_reader_stats;
 	mutable hxb_writer_config : HxbWriterConfig.t option;
 }
@@ -844,6 +845,7 @@ let create compilation_step cs version args display_mode =
 		has_error = false;
 		report_mode = RMNone;
 		is_macro_context = false;
+		hxb_reader_api = None;
 		hxb_reader_stats = HxbReader.create_hxb_reader_stats ();
 		hxb_writer_config = None;
 	} in
@@ -896,6 +898,7 @@ let clone com is_macro_context =
 		overload_cache = new hashtbl_lookup;
 		module_lut = new module_lut;
 		fake_modules = Hashtbl.create 0;
+		hxb_reader_api = None;
 		hxb_reader_stats = HxbReader.create_hxb_reader_stats ();
 		std = null_class;
 		empty_class_path = new ClassPath.directory_class_path "" User;