Refactor .py signatures infra

[maxtropets]

Motto: consolidate signature verification in one place, and benefit from it greatly when introducing PQC COSE signatures in the future.

I still plan to keep a split for verifying classical/cose, but for cose we'll extend the table itself in the future and will iterate over multiple cose signatures instead, and will try to get rid of classical signatures somewhere in the future.

[Copilot]

Pull request overview

This PR refactors the Python-side ledger signature handling by introducing a dedicated ccf.signatures module and updating tests/utilities to use a shared “is this a signature transaction?” predicate and shared parsing/verification helpers. It keeps external compatibility by re-exporting legacy names from ccf.ledger.

Changes:

• Added python/src/ccf/signatures.py to centralize signature table constants, parsing, and primitive verification helpers.
• Refactored python/src/ccf/ledger.py’s LedgerValidator signature validation to use the new shared helpers, while re-exporting prior public symbols for backwards compatibility.
• Updated multiple tests and Python utilities to detect signature transactions via is_signature_transaction() rather than ad-hoc table checks/string matching.

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Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/recovery.py	Uses ccf.signatures.is_signature_transaction() for signature tx detection in recovery corruption/selection helpers.
tests/reconfiguration.py	Switches signature parsing to parse_classical_signatures() and uses structured payload fields.
tests/governance_history.py	Refactors signature schema/position checks to use shared signature-tx detection + structured parsing.
tests/e2e_operations.py	Consolidates signature transaction detection via ccf.signatures.is_signature_transaction().
python/src/ccf/split_ledger.py	Uses shared signature-tx detection when splitting ledgers around signature transactions.
python/src/ccf/signatures.py	New module defining signature table registry, parsers, and primitive verifiers.
python/src/ccf/ledger.py	Re-exports signature APIs for compatibility and refactors validator signature verification flow.
python/src/ccf/ledger_viz.py	Uses shared signature-tx detection for labeling signature entries in visualization.

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

[maxtropets]

@copilot how come if the check in l688 does exactly that?