Python package tidy ups

[achamayou]

Improve pyproject.toml (use the native Python version numbers directly, set the license the modern way, correct dependencies), and modernise some patterns in our code that are unnecessarily old-fashioned.

[Copilot]

Pull request overview

This PR updates the Python package metadata to be more PEP-compliant and modernises several Python modules/tests (typing syntax, cryptography API usage), plus minor script cleanup around release-note validation.

Changes:

• Update python/pyproject.toml metadata (PEP 440 version format, SPDX-style license fields, dependency list tweaks).
• Modernise Python code to use built-in generics / PEP 604 unions and remove deprecated cryptography backend usage.
• Small cleanup/fixups in release tooling and helper scripts.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
scripts/extract-release-notes.py	Adjusts version comparison against pyproject.toml for changelog validation.
python/utils/submit_recovery_share.sh	Fixes/help text output for usage instructions.
python/tests/test_cose_sign.py	Removes deprecated default_backend() usage in cryptography calls.
python/src/ccf/tx_id.py	Updates optional typing to `str
python/src/ccf/split_ledger.py	Migrates typing from List[...] to list[...].
python/src/ccf/receipt.py	Migrates typing from List[...] to list[...].
python/src/ccf/merkletree.py	Modernises class definition (class MerkleTree:).
python/src/ccf/ledger_viz.py	Updates optional typing to `str
python/src/ccf/ledger_code.py	Removes accidental tuple creation in validator assignment.
python/src/ccf/ledger.py	Modernises typing and removes deprecated cryptography backend usage.
python/src/ccf/cose.py	Removes deprecated cryptography backend usage and modernises typing.
python/src/ccf/_versionifier.py	Uses removeprefix and renames helper to underscore-prefixed function.
python/pyproject.toml	Switches to PEP 440 dev version, adds SPDX-style license fields, updates dependencies.