Add extensions in compiled CTS/MTS

[egasimus]

@hackbg/4mat is compiled and published using @hackbg/ubik. When installed in a Deno project, at the path node_modules/.deno/@hackbg+4mat@3.1.2/node_modules/@hackbg/4mat/4mat.dist.d.mts is found the reexport statement:

export * from './4mat.browser'; 

which should instead be:

export * from './4mat.browser.dist.mts'; 

because otherwise Deno fails to see the reexported items.