pyproject.toml: Enable mypy.warn_redundant_casts

Add warn_redundant_casts = true to the mypy configuration template.
This rule detects casts that mypy proves unnecessary, helping to
clean up redundant type casts that clutter the codebase.

This is one of the boolean-flag rules being gradually adopted from
the stricter mypy profile in /tmp/pyproject.toml. It produces just
1 error during initial rollout.

Assisted-by: unsloth/Qwen3.6-35B-A3B-GGUF:IQ4_NL and pi.dev 0.81.1
Signed-off-by: Jan Lindemann <jan@janware.com>

conf/templates/pyproject.toml

@@ -2,6 +2,8 @@
 
   {mypypath}
 
+  warn_redundant_casts = true
+
   enable_error_code = [
     "explicit-override",
     "ignore-without-code",