Function signerAvailability

signerAvailability(
signer: ISigner | undefined,
method: MessagingEncryption,
): ProviderAvailability
Whether a signer can carry messages that need method.
Parameters
- signer: ISigner | undefined
  The active account's signer, or undefined while nobody is signed in.
- method: MessagingEncryption
  The encryption the provider uses.
Returns ProviderAvailability
Available, or unavailable with sign-in-required or signer-cannot-encrypt.
Example
```
signerAvailability(undefined, 'nip44'); // { available: false, reason: 'sign-in-required' }
signerAvailability(new PrivateKeySigner(), 'nip44'); // { available: true }
```