Function save_wallet 

pub fn save_wallet(
    path: &str,
    keypair_bytes: &[u8],
    force: bool,
) -> Result<PathBuf, String>

Save raw keypair bytes to a file in Solana CLI JSON byte-array format.

The file is written with 0o600 permissions (owner read/write only). Refuses to overwrite an existing file unless force is true.

Errors

Returns a human-readable error string if the file cannot be written or already exists without force.