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Is your feature request related to a problem? Please describe.
clj-kondo currently doesn't warn about duplicate symbols in :exclude clauses within ns forms. This can lead to redundant and potentially confusing namespace declarations, similar to how duplicate refers are already detected.

Describe the solution you'd like
Add a new linter (e.g., :duplicate-exclude) that detects and warns about duplicate symbols in:

1. (:refer-clojure :exclude [sym1 sym2 sym1]) - duplicate in refer-clojure exclude
2. (:require [some.ns :exclude [sym1 sym2 sym1]]) - duplicate in require exclude

The warning should be similar to the existing :duplicate-refer linter.

Describe alternatives you've considered

• Keep relying on manual code review to catch duplicates

Additional context
Currently, clj-kondo successfully detects duplicate refers:

;; This produces: "Duplicate refer: split"
(ns foo (:require [clojure.string :refer [split split]]))

But does not detect duplicate excludes:

;; This produces no duplicate warning, only "Unused excluded var: map"
(ns foo (:refer-clojure :exclude [map map]))

The new linter would provide consistency with the existing duplicate detection capabilities and help catch redundant namespace declarations early.