style block number with click-to-copy and etherscan link

Add blockNumberHtml() following the same pattern as txHashHtml() and
toAddressHtml(): dashed-underline click-to-copy text plus an external
Etherscan link icon (etherscan.io/block/{number}).

Closes #99

src/popup/views/txStatus.js

@@ -50,15 +50,6 @@ function toAddressHtml(address) {
     return `<div class="flex items-center">${dot}<span class="break-all underline decoration-dashed cursor-pointer" data-copy="${escapeHtml(address)}">${escapeHtml(address)}</span>${extLink}</div>`;
 }
 
-function txHashHtml(hash) {
-    const link = `https://etherscan.io/tx/${hash}`;
-    const extLink = `<a href="${link}" target="_blank" rel="noopener" class="inline-flex items-center">${EXT_ICON}</a>`;
-    return (
-        `<span class="underline decoration-dashed cursor-pointer break-all" data-copy="${escapeHtml(hash)}">${escapeHtml(hash)}</span>` +
-        extLink
-    );
-}
-
 function blockNumberHtml(blockNumber) {
     const num = String(blockNumber);
     const link = `https://etherscan.io/block/${num}`;
@@ -69,6 +60,15 @@ function blockNumberHtml(blockNumber) {
     );
 }
 
+function txHashHtml(hash) {
+    const link = `https://etherscan.io/tx/${hash}`;
+    const extLink = `<a href="${link}" target="_blank" rel="noopener" class="inline-flex items-center">${EXT_ICON}</a>`;
+    return (
+        `<span class="underline decoration-dashed cursor-pointer break-all" data-copy="${escapeHtml(hash)}">${escapeHtml(hash)}</span>` +
+        extLink
+    );
+}
+
 function attachCopyHandlers(viewId) {
     document
         .getElementById(viewId)