diracx-tasks: consider function_load or evalsha

We currently rely on `redis.eval` to evaluate the `lua` scripts.

When designing the system, we came accross `function_load` and `evalsha` to run the `lua` scripts, sort of as a stored procedure, instead of evaluating the script everytime.
This could possibly help performance in case we ever struggle.

Start by locating the diracx-tasks code that currently calls redis.eval and trace how its Lua scripts are supplied and executed. Compare the implications of Redis function_load and evalsha for this usage, including whether either improves performance, and document a clear recommendation or implementation scope as the outcome.

Written by the indexing model from the issue text.