feat: multiple conversions

[Jay-Karia]

Adds a new feature: Multiple Conversions
Can convert and get multiple commands by calling the function single time

1. One to many (convert one command into multiple package managers' equivalent)

convertMultiple("npm i next", ["pnpm", "bun"])
// ["pnpm add next", "bun add next"]

2. Many to one (convert many commands into one 1 package manager's equivalent)

convertMultiple(["npm i eslint", "pnpm add react"], "yarn")
// ["yarn add eslint", "yarn add react"]

3. Many to many (convert many commands into multiple package managers' equivalent)

convertMultiple(["bun add rollup", "npm i express"], ["yarn", "pnpm"])
/*
[
    ["yarn add rollup", "yarn add express"], 
    ["pnpm add rollup", "pnpm add express"]
]
*/

Closes #56

[Jay-Karia]

@nebrelbug Can you please review this ?

[nebrelbug]

@Jay-Karia I appreciate this PR, but as of right now I'm not convinced that it adds enough value to the package to make it worth the increased size and maintenance. It seems to me like this could be implemented fairly simply by developers. I'll leave this open for a while to see if there's strong interest from the community.