Fix decode/1 crash on non-JSON strings from search input

[mcass19]

Hi, it's me again :). Keep the nice work and library!!!

Problem

LiveSelect.decode/1 crashes with a Jason.DecodeError when the value passed to it is a plain string that isn't valid JSON.

This happens when a form with phx-change fires while the user is typing in the LiveSelect text input but hasn't made a selection yet. The raw search text (e.g., "Glon") arrives as the field value, and decode/1 crashes because unquoted text is not valid JSON.

** (Jason.DecodeError) unexpected byte at position 0: 0x47 ("G")
    (jason 1.4.4) lib/jason.ex:92: Jason.decode!/2
    (elixir 1.19.0) lib/kernel.ex:2983: anonymous fn/2 in Kernel.update_in/3
    (elixir 1.19.0) lib/map.ex:965: Map.get_and_update/3
    (elixir 1.19.0) lib/kernel.ex:2983: Kernel.update_in/3

How to reproduce

1. Create a form with phx-change="validate" containing a LiveSelect field (e.g., user_id)
2. In the handle_event("validate", ...), call LiveSelect.decode/1 on the field value as shown in the docs:
   params = update_in(params, ~w(my_form my_field), &LiveSelect.decode/1)
3. Type text into the LiveSelect search input (e.g., "Glon") without selecting an option
4. Trigger a form change event (e.g., by changing another field, or by the _target hitting the LiveSelect field)

The raw search text arrives as the field value, and decode/1 crashes.

Root cause

There is an asymmetry between encode and decode.
In component.ex, encode/1 has a fast path that skips JSON encoding for simple types. But decode/1 in live_select.ex always calls json.decode! on any non-nil, non-empty value.

This means values that were never JSON-encoded (simple strings, raw text from typing) get json.decode! called on them, which crashes.

Fix

Rescue decode errors and return the raw value as-is, mirroring how encode/1 passes simple types through without encoding.

This way, valid JSON is decoded as before, and non-JSON strings pass through to the changeset which handles validation normally.

There's a test added that fails without the fix.

[maxmarcon]

Thanks for this. I will look into this as soon as I have some time