[ref] pkstl: use same config object for all modes

lib/tools/pkstl/src/agreement.rs

lib/tools/pkstl/src/complete.rs

lib/tools/pkstl/src/complete/serde/serializer.rs

lib/tools/pkstl/src/config.rs

lib/tools/pkstl/src/encryption.rs

lib/tools/pkstl/src/encryption/chacha20_poly1305_aead.rs

lib/tools/pkstl/src/lib.rs

lib/tools/pkstl/src/minimal.rs

lib/tools/pkstl/tests/complete_mode.rs

lib/tools/pkstl/tests/complete_serde_mode.rs

lib/tools/pkstl/tests/minimal_mode.rs