trim the leading forward-slashes at the beginning of a string.

import { assertEquals } from "jsr:@std/assert"

// aliasing our functions for brevity
const eq = assertEquals, fn = trimStartSlashes

eq(fn("///a/b.txt//"), "a/b.txt//")
eq(fn("/.//a/b.txt//"), ".//a/b.txt//")
eq(fn(".///../a/b.txt//"), ".///../a/b.txt//")
eq(fn("file:///a/b.txt//"), "file:///a/b.txt//")