fix: type resolution in node16 environments

[samuelstroschein]

3251584 introduced a bug in node16 environments. Line

magicast/helpers.d.ts

Line 1 in 3251584

export * from "./dist/helpers.d";

must include the file extension. Thus, `export * from "./dist/helpers.d.ts";

[codecov]

Codecov Report

Merging #60 (f673edb) into main (c6897eb) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #60   +/-   ##
=======================================
  Coverage   92.05%   92.05%           
=======================================
  Files          24       24           
  Lines        1612     1612           
  Branches      293      293           
=======================================
  Hits         1484     1484           
  Misses        128      128