chore: remove dead exports and share copied view helpers (closes #168)

AddressDetail and AddressToken defined their own isoDate() and
timeAgo(), hiding the shared pair in helpers.js, so a fix there would
not have reached them. The copies were identical and are deleted;
blockieHtml() and tokenLabel(), each defined twice, move to helpers.js.
A new test shows the history rows and the transaction detail view
write the time with the shared pair.

Deleted as never called: explorerLink(), ETHEREUM_SEPOLIA_CHAIN_ID,
getWalletValue() and getTotalValue() with their tests. Home's "Total:"
is the active address's total, as README.md already says.
addressColor() and etherscanAddressUrl() are no longer exported.

Model: opus-5-5

tests/support/popupBoot.js

@@ -253,8 +253,6 @@ async function bootPopup(stored, options) {
         formatUsd: () => "",
         formatAddressTotal: () => "",
         getAddressValue: () => ({ usd: null, partial: false }),
-        getWalletValue: () => ({ usd: null, partial: false }),
-        getTotalValue: () => ({ usd: null, partial: false }),
     }));
     jest.doMock("../../src/shared/balances", () => ({
         fetchTokenBalances: jest.fn(async () => []),