Optimize glob filtering

[Katsute]

Replace https://github.com/KatsuteDev/Background/blob/d0acae680ca0e9e928574e98c7c89f81a3dc9e01/src/lib/glob.ts#L28-L34

with

const filter: (v: string) => boolean = (v : string) => {
    const ext: string = extname(v).slice(1); // remove the dot at the beginning
    return extensions().includes(ext);
}