fix(cli): incorrect/unnecessary passphrase assumptions

[0xferrous]

What

Don't make empty passphrase assumptions in wallet create/import/export/decrypt.

Why

read_passphrase currently:

1. tries to read passphrase from env vars OWS_PASSPHRASE, LWS_PASSPRASE.
2. checks if it is an interactive terminal, if it is, it prompts the user for passphrase
3. if it is not an interactive terminal, it assumes passphrase to be "".

Given this, there is no need for us to assume:

1. Empty passphrases for ows wallet import, ows wallet create. This assumption creates poor security for human users.
2. Empty passphrase while decrypting the signing key, this assumption causes 2x the time for all wallets encrypted without "", even in cases when OWS_PASSPHRASE was explicitly set.

Closes #

Testing

• cargo test --workspace passes
• cargo clippy --workspace -- -D warnings is clean
• npm test passes (if Node bindings changed)
• Tested manually with ows CLI

Notes

Anything reviewers should know.

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