Split test vectors into three csv files + Add new vectors

[siv2r]

Fixes #9 Addresses #10

Currently, test vectors for all the APIs are present in a single CSV file. This PR splits them into two CSV files.

1. presig_vectors.csv: contains the test vectors for the schnorr_presig_signand schnorr_extract_adaptor APIs
2. adapt_secadaptor_vectors.csv: contains the test vectors for the schnorr_adaptand schnorr_extract_secadaptor APIs

Todo List:

• [x] add a note in each CSV file that explains what the result column represents
• [x] improve presig vectors
• [x] improve adapt vectors
• [x] improve secadaptor vectors
• [x] fix reference.py test against vectors

[siv2r]

This pull request is ready for review. I tried to split this into multiple PRs, but the changes depended on each other, so I kept them together.

Currently, the test_pre_sign_generation(), test_pre_sign_nonce(), and test_pre_sign_nonce_without_auxrand() tests (in reference.py) throw mypy errors because I introduced the PlainPk and XonlyPk types.

Should we move these tests into a new file or remove them altogether? These tests are incomplete, and I don’t see such tests in other BIP reference codes (except here).

[ZhePang]

Great Job! Will add more test vectors to increase the test coverage.