Merge bitcoin/bitcoin#26275: Fix crash on deriveaddresses when index is 2147483647 (2^31-1)

9153ff3e27 rpc: add non-regression test about deriveaddresses crash when index is 2147483647 (muxator)
addf9d6502 rpc: fix crash in deriveaddresses when derivation index is 2147483647 (muxator)

Pull request description:

  This PR is a proposal for fixing #26274 (better described there).

  The problem is due to a signed int wrapping when the `index` parameter of the `deriveaddresses` RPC call has the value `2^31-1`.

  ```C++
  for (int i = range_begin; i <= range_end; ++i) {
  ```

  * the first commit adds a "temporary" test case (`test/functional/rpc_deriveaddresses_crash.py`) that shows the crash, and can be used to generate a core dump;
  * the second commit fixes the problem giving an explicit size to the `i` variable in a for loop, from `int` to `int64_t`. The same commit also removes the ephemeral test case and adds a passing test to `test/functional/rpc_deriveaddresses.py`, in order to prevent future regressions.

  This is my first submission to this project and I do not know its conventions. Please advise if something needs to be changed.

ACKs for top commit:
  achow101:
    ACK 9153ff3e27

Tree-SHA512: 0477b57b15dc2c682cf539d6002f100d44a8c7e668041aa3340c39dcdbd40e083c75dec6896b6c076b044a01c2e5254272ae6696d8a1467539391926f270940a

src/rpc/output_script.cpp

@@ -273,7 +273,7 @@ static RPCHelpMan deriveaddresses()
 
             UniValue addresses(UniValue::VARR);
 
-            for (int i = range_begin; i <= range_end; ++i) {
+            for (int64_t i = range_begin; i <= range_end; ++i) {
                 FlatSigningProvider provider;
                 std::vector<CScript> scripts;
                 if (!desc->Expand(i, key_provider, scripts, provider)) {