Use static storage for path_buf

It is safe to re-use this buffer since the data in the buffer is
duplicated in recursive calls to findTags. So there is no need to blow
up our stack (which could be quite large with recursive invocations) by
allocating this large array on each call.

src/Tags.zig

@@ -81,6 +81,11 @@ allocator: std.mem.Allocator,
 entries: EntryList,
 visited: std.StringHashMap(void),
 
+/// Static buffer for writing full paths.
+///
+/// Data in this buffer is duplicated when passed to findTags.
+var path_buf: [std.fs.MAX_PATH_BYTES]u8 = undefined;
+
 pub fn init(allocator: std.mem.Allocator) Tags {
     return Tags{
         .allocator = allocator,
@@ -141,8 +146,6 @@ pub fn findTags(self: *Tags, fname: []const u8) anyerror!void {
     var ast = try std.zig.Ast.parse(allocator, source, .zig);
     defer ast.deinit(allocator);
 
-    var path_buf: [std.fs.MAX_PATH_BYTES]u8 = undefined;
-
     const tags = ast.nodes.items(.tag);
     const tokens = ast.nodes.items(.main_token);
     const datas = ast.nodes.items(.data);