Don't require getopt to be installed by brew on macOS for Nix users

Other changes:

* Add/Update copyright banners
* Add post-review comment for #5719

beacon_chain/networking/eth2_network.nim

@@ -1964,6 +1964,14 @@ proc p2pProtocolBackendImpl*(p: P2PProtocol): Backend =
               codecNameLit))
 
   result.implementProtocolInit = proc (p: P2PProtocol): NimNode =
+    # TODO
+    # This current approach is not building on good foundations.
+    # Incrementing a global variable at compile-time fundamentally at odds with
+    # incremental compilation (because a recompile that doesn't revisit the whole
+    # program will mess up the counting and create duplicate indices).
+    # A better approach would build upon the `macrocache` module from the standard
+    # library, which is compatible with incremental compilation:
+    # https://nim-lang.org/docs/macrocache.html
     var id {.global.}: int
     let tmp = id
     id += 1

installer/nix/shell.nix

@@ -1,3 +1,10 @@
+# beacon_chain
+# Copyright (c) 2023-2024 Status Research & Development GmbH
+# Licensed and distributed under either of
+#   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
+#   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
+# at your option. This file may not be copied, modified, or distributed except according to those terms.
+
 { pkgs ? import <nixpkgs> {}}:
 let
   mkdocs-packages = ps: with ps; [
@@ -16,6 +23,7 @@ mkShell {
     git
     git-lfs
     gnumake
+    getopt
 
     # For the local simulation
     openssl # for generating the JWT file
@@ -34,6 +42,7 @@ mkShell {
     # will erase `-march=native` because this introduces impurity in the build.
     # For the purposes of compiling Nimbus, this behavior is not desired:
     export NIX_ENFORCE_NO_NATIVE=0
+    export USE_SYSTEM_GETOPT=1
 
     figlet "Welcome to Nimbus-eth2"
   '';

scripts/launch_local_testnet.sh

@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 
-# Copyright (c) 2020-2023 Status Research & Development GmbH. Licensed under
+# Copyright (c) 2020-2024 Status Research & Development GmbH. Licensed under
 # either of:
 # - Apache License, version 2.0
 # - MIT license
@@ -34,7 +34,7 @@ PIDS_TO_WAIT=""
 ####################
 
 GETOPT_BINARY="getopt"
-if [[ "${OS}" == "macos" ]]; then
+if [[ "${OS}" == "macos" && "$USE_SYSTEM_GETOPT" != "1" ]]; then
   # Without the head -n1 constraint, it gets confused by multiple matches
   GETOPT_BINARY=$(find /opt/homebrew/opt/gnu-getopt/bin/getopt /usr/local/opt/gnu-getopt/bin/getopt 2> /dev/null | head -n1 || true)
   [[ -f "$GETOPT_BINARY" ]] || { echo "GNU getopt not installed. Please run 'brew install gnu-getopt'. Aborting."; exit 1; }