fix io.read & file:read signature

[fperrad]

No description provided.

[github-actions]

Teal Playground URL: https://718--teal-playground-preview.netlify.app

[hishamhm]

I think it's better to declare this as a polymorphic function so we don't have to use casts in the most common cases. I will try my hand at an alternative implementation, but thank you for the PR pointing out the issue!

[fperrad]

From Reference Manuals, available formats are:

• Lua 5.1: "*n", "*a", "*l"
• Lua 5.2: "*n", "*a", "*l", "*L"
• Lua 5.3: "n", "a", "l", "L"
• Lua 5.4: "n", "a", "l", "L"

The starting * is allowed in implementation of Lua 5.3 & 5.4, only for compatibily reason (see function g_read() in liolib.c).

It could be nice that Teal allows only Lua 5.3/4 formats, and the * will be added by the generation targeting Lua 5.1/2.