fix(core): remove circular import in store.ts & MnemonicWallet

[No-Cash-7970]

I haven't encountered a bug this gnarly in a while. 🤣

The circular import: src/wallets/mnemonic imports src/store, which imports a few types from src/wallets. The src/wallets/mnemonic is still loaded when src/store imports src/wallet despite nothing from src/wallets/mnemonic being used.

In short, src/wallets/mnemonic imports src/store, which indirectly imports src/wallets/mnemonic.

This circular import caused an odd issue where the persisted mnemonic had "undefined_mnemonic" as the key in localStorage because LOCAL_STORAGE_KEY constant (defined in src/store.ts before building the package) was used before it was defined in the dist/index.js build output file. The bundler got confused by the circular import and put the modules in the resulting dist/index.js in the wrong order.