Merge bitcoin/bitcoin#32100: doc: clarify the documentation of Assume assertion

329a0dcdafe05002f662e8737a76bfdeaba9a3ed doc: clarify the documentation of `Assume` (ismaelsadeeq)

Pull request description:

  An Expression inside `Assume` may be optimized away in production builds when the compiler proves they are side-effect-free.
  This use case is demonstrated in #31363 and is suggested to be documented in https://github.com/bitcoin/bitcoin/pull/31363#issuecomment-2736410023.

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doc/developer-notes.md

@@ -460,7 +460,10 @@ other input.
   safely continue even if the assumption is violated. In debug builds it
   behaves like `Assert`/`assert` to notify developers and testers about
   nonfatal errors. In production it doesn't warn or log anything, though the
-  expression is always evaluated.
+  expression is always evaluated. However, if the compiler can prove that
+  an expression inside `Assume` is side-effect-free, it may optimize the call away,
+  skipping its evaluation in production. This enables a lower-cost way of
+  making explicit statements about the code, aiding review.
    - For example it can be assumed that a variable is only initialized once,
      but a failed assumption does not result in a fatal bug. A failed
      assumption may or may not result in a slightly degraded user experience,