Fix Chrome prefetch main_frame & outermost_frame

[agoodkind]

Changes

Added two new functions:

1. getTrueTabDomain(tabId) - Fetches the actual domain from the tab's URL (source of truth from the address bar)
2. isMainTabUrl(details) - Validates if a request is truly for the main frame by comparing the request's domain against the tab's actual domain

Modified two locations:

1. chrome.webRequest.onBeforeRequest - Replaced simple type check with await isMainTabUrl(details)
2. chrome.webRequest.onBeforeRedirect - Replaced simple type check with await isMainTabUrl(details)

What this fixes

When Chrome prefetches links, it sends requests with type: "main_frame", which previously caused mainDomain to be overwritten incorrectly. The fix validates that the request's domain matches the tab's actual URL before treating it as a main frame navigation, preventing prefetch requests from corrupting the extension's state.

Before:

https://github.com/user-attachments/assets/eefd8d31-d122-44d2-9552-e5def210c026

After:

https://github.com/user-attachments/assets/aacb1ea4-b19d-4aeb-bf36-e77693b84a7a

[agoodkind]

@pmarks-net This fixes https://github.com/pmarks-net/ipvfoo/issues/71

[pmarks-net]

I found a preliminary solution. It's called from the same places as await isMainTabUrl in your PR.

function isProperMainFrame(details) {
  if (details.type == "main_frame" || details.type == "outermost_frame") {
    if (details.documentId) {
      // It seems that a main_frame request with a documentId refers to some kind
      // of prefetch, rather than a top-level navigation to a new URL.
      console.log("Preloaded main_frame?", details.url);
      return false;
    }
    return true;
  }
  return false;
}

Demo: https://www.google.com/search?q=real+estate

background.js:951 Preloaded main_frame? https://www.realtor.com/...
background.js:951 Preloaded main_frame? https://www.zillow.com/...

IPvFoo shows "www.realtor.com 2001:4860:4802:34::9d" and "www.zillow.com 2001:4860:4802:34::9d", which suggests that the requests are being proxied by Google. I should probably add a P/prefetch icon next to the address, because otherwise the results could be misleading. Neither of those sites actually support IPv6.