first pass at filesystem evaluation in eval system

src/file_stream/file_stream.h

@@ -13,6 +13,7 @@ struct FS_Node
   FS_Node *next;
   String8 path;
   U64 timestamp;
+  U64 size;
   B32 is_working;
 };
 
@@ -83,6 +84,7 @@ internal U64 fs_change_gen(void);
 internal U128 fs_hash_from_path(String8 path, U64 endt_us);
 internal U128 fs_key_from_path(String8 path);
 internal U64 fs_timestamp_from_path(String8 path);
+internal U64 fs_size_from_path(String8 path);
 
 ////////////////////////////////
 //~ rjf: Streamer Threads