Use Session as a container for cross-frame resources

The introduction of frames means that data is no longer tied to a specific Page
or Context. 255b9a91cc introduced Origins for
v8 values shared across frames of the same origin. The commit highlighted the
lifetime mismatched that we now have with data that can outlive 1 frame. A
specific issue with that commit was the finalizers were still Context-owned.
But like any other piece of data, that isn't right; aside from modules, nothing
should be context-owned.

This commit continues where the last left off and moves finalizers from Context
to Origin. This is done in a separate commit because it introduces significant
changes. Currently, finalizers take a *Page, but that's no longer correct. A
value created in one Page, can outlive the Page. We need another container. I
original thought to use Origin, but that isn't know to CDP/MCP. Instead, I
decide to enhance the Session.

Session is now the owner of the page.arena, the page.factory and the
page.arena_pool. Finalizers are given a *Session which they can use to release
their arena.

src/mcp/tools.zig

@@ -92,7 +92,8 @@ const ToolStreamingText = struct {
             },
             .links => {
                 if (Selector.querySelectorAll(self.page.document.asNode(), "a[href]", self.page)) |list| {
-                    defer list.deinit(self.page);
+                    defer list.deinit(self.page._session);
+
                     var first = true;
                     for (list._nodes) |node| {
                         if (node.is(Element.Html.Anchor)) |anchor| {