Large integers are not serialized and written properly in serde/fs

[Crystalflxme]

Reproduction:

# testing.toml
testValue = 5208470842

-- testing.luau
local serde = require("@lune/serde")
local fs = require("@lune/fs")

local testing = serde.decode("toml", fs.readFile("testing.toml"))
fs.writeFile(
	`result.json`,
	serde.encode("json", {
		testValue = testing.testValue,
	})
)

Running lune testing will result in the following json file.

{"testValue":5208470842.0}

In most cases, it seems to preserve integers. However, with larger integers, it appears to append .0. This can cause issues if the resulting file requires integers.