refactor: improve email copy with MapSet, RFC 5322 commas, and cond

Performance optimization, RFC-compliant separator, better tests

lib/mv_web/live/member_live/index.html.heex

@@ -3,18 +3,18 @@
     {gettext("Members")}
     <:actions>
       <.button
-        :if={Enum.any?(@members, &(&1.id in @selected_members))}
+        :if={Enum.any?(@members, &MapSet.member?(@selected_members, &1.id))}
         id="copy-emails-btn"
         phx-hook="CopyToClipboard"
         phx-click="copy_emails"
         aria-label={gettext("Copy email addresses of selected members")}
       >
         <.icon name="hero-clipboard-document" />
-        {gettext("Copy emails")} ({Enum.count(@members, &(&1.id in @selected_members))})
+        {gettext("Copy emails")} ({Enum.count(@members, &MapSet.member?(@selected_members, &1.id))})
       </.button>
       <.button
-        :if={Enum.any?(@members, &(&1.id in @selected_members))}
-        href={"mailto:?bcc=#{@members |> Enum.filter(&(&1.id in @selected_members and &1.email)) |> Enum.map(& &1.email) |> Enum.join(",")}"}
+        :if={Enum.any?(@members, &MapSet.member?(@selected_members, &1.id))}
+        href={"mailto:?bcc=#{@members |> Enum.filter(&(MapSet.member?(@selected_members, &1.id) && &1.email)) |> Enum.map(& &1.email) |> Enum.join(",")}"}
         aria-label={gettext("Open email program with BCC recipients")}
       >
         <.icon name="hero-envelope" />
@@ -51,7 +51,7 @@
           type="checkbox"
           name="select_all"
           phx-click="select_all"
-          checked={Enum.sort(@selected_members) == Enum.map(@members, & &1.id) |> Enum.sort()}
+          checked={MapSet.equal?(@selected_members, @members |> Enum.map(& &1.id) |> MapSet.new())}
           aria-label={gettext("Select all members")}
           role="checkbox"
         />
@@ -63,7 +63,7 @@
         name={member.id}
         phx-click="select_member"
         phx-value-id={member.id}
-        checked={member.id in @selected_members}
+        checked={MapSet.member?(@selected_members, member.id)}
         phx-capture-click
         phx-stop-propagation
         aria-label={gettext("Select member")}