fix: escape magic characters in module path patterns

Addresses loader errors when encountering hyphens in module paths. To reproduce, try adding e.g. `<rtp>/plugin/my-plugin.fnl`. (There's room to escape more characters from the intersection of legal module names ↔ pattern magic characters, but they'd possibly verge on likely errors / careful reproductions of built-in loader edge cases, v.s. things which people would legitimately expect to work.)