Migrate to internal creation emptiness checks

Pina’s typed creation builders now enforce emptiness themselves and return AccountAlreadyInitialized when the target storage holds any nonzero byte. The deny-by-default require_empty_before_init lint is retired.

Remove the lint from pina.toml

Delete the [lints] entry; the CLI now rejects the unknown name.

[lints]
# remove:
# require_empty_before_init = "deny"

Remove manual pre-creation assertions

Delete assert_empty() calls that exist only immediately before a typed creation builder. Keep assert_empty() calls that guard other operations, such as raw CreateAccount allocations or token-account creation, where the typed builders are not involved.

#![allow(unused)]
fn main() {
// before
self.state.assert_empty()?;
CreateProgramAccountWithBump { account: self.state, /* .. */ }.invoke_with::<State>(/* .. */)?;

// after
CreateProgramAccountWithBump { account: self.state, /* .. */ }.invoke_with::<State>(/* .. */)?;
}

Error behavior is preserved: the builders return the same AccountAlreadyInitialized error the manual assertions produced.