upstream to Mathlib — general BitVec XOR cancellation lemma.

[github-actions]

XOR by a fixed mask is self-inverse on BitVec: c = k ^^^ m ↔ c ^^^ m = k. -/

cslib/Cslib/Crypto/Protocols/PerfectSecrecy/Internal/OneTimePad.lean

Lines 27 to 28 in c1f2e8e

	-- TODO: upstream to Mathlib — general BitVec XOR cancellation lemma.
	/-- XOR by a fixed mask is self-inverse on `BitVec`: `c = k ^^^ m ↔ c ^^^ m = k`. -/