cache decorator confuses positional tuples with keyword arguments

Describe the bug

@cl.cache can return the result of a different call when a positional tuple matches a keyword argument's key/value pair.

To reproduce

Run against current main (190ea74239d9e84b26e7c91bc2882dd038942564):

import chainlit as cl

@cl.cache
def identity(value):
    return value

print(identity(("value", 1)))
print(identity(value=1))

Actual output:

('value', 1)
('value', 1)

Expected output:

('value', 1)
1

Reversing the call order also reproduces the problem: both calls return 1.

Cause

backend/chainlit/cache.py concatenates positional arguments and sorted keyword pairs into a single tuple. Both calls therefore produce the same cache key, even though their argument values differ.

Keeping the function, positional arguments, and keyword pairs as separate parts of the key fixes the collision without changing the public API or locking behavior.

Environment

Windows, Python 3.13.7, Chainlit source version 2.12.0.

This is distinct from #2985 and its merged fix #2987, which addressed collisions between different functions with the same name. I have a fix and a regression test covering both call orders and repeated cache hits.