[Feature request] Implicit casts for common conversions

I got some code for parsing command line flags/user inputs that commonly uses patterns like this

---@return string ...
local function strsplit(str, sep) end

local a, b, c = strsplit(userinput, ",")
b = tonumber(b) or 0 -- error:  This variable is defined as type `string`. Cannot convert its type to `number`

The fix is to define b as string|number in the declaration, but it's a bit cumbersome, especially if I just want b as a number:

local a,
---@type number|string
b, c = strsplit(userinput, ",")

So it would be nice if common type conversion patterns like this could be recognized automatically and either allow the cast or infer the type as string|number from the beginning.

Edit: See comment below, the implicit cast is already happening, this is really about type inference based on later assignments. Which may or may not be a good idea.

Empieza por rastrear el comportamiento existente de implicit-cast y type-inference descrito en el issue, especialmente cómo las asignaciones posteriores afectan a una declaración de variable anterior. Define las reglas de inferencia previstas y verifícalas con el ejemplo de análisis de la línea de comandos; el trabajo estará terminado cuando haya un comportamiento acordado y pruebas que cubran el tipo inferido resultante.