Update Norbeck; various BB tweaks

[zmoon]

• update Norbeck zip archive URL to the new 2026-01 version (2026-01-27 in site footer)
• BB s-tunes is currently RTF (may be temporary)
• BB now has HTTPS
• organization of the BB tunefolders is changing, made current updates but also allowing the test to fail for now

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.27%. Comparing base (1646b77) to head (921aca7).
⚠️ Report is 16 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #96   +/-   ##
=======================================
  Coverage   94.26%   94.27%           
=======================================
  Files          15       15           
  Lines        1745     1747    +2     
=======================================
+ Hits         1645     1647    +2     
  Misses        100      100           

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[Copilot]

Pull request overview

This PR updates the Norbeck ABC tune archive URL to the latest version (2026-01) and makes several changes to accommodate updates to Bill Black's Irish Traditional Tune Library, which has migrated to HTTPS and temporarily changed some files to RTF format.

Changes:

• Updated Norbeck zip archive URL from hn202110.zip to hn202601.zip
• Migrated all Bill Black URLs from HTTP to HTTPS
• Added support for RTF file format for Bill Black's s-tunes-2 file with appropriate processing logic
• Updated Bill Black tunefolder subfolder structures, particularly for O'Farrell's Pocket Companion collection
• Added xfail markers to tests for Bill Black features that are currently in flux
• Enhanced test_the_session_get_member_sets_multipage with orderby parameter and more specific assertions

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
tests/test_sources.py	Updated expected Norbeck tune count, added xfail markers for Bill Black tests in flux, updated regex to match RTF files, and enhanced the_session test with ordering and additional assertions
pyabc2/sources/norbeck.py	Updated download URL to latest Norbeck archive version (2026-01)
pyabc2/sources/bill_black_tunefolders.py	Migrated all URLs from HTTP to HTTPS, updated subfolder structures for various collections, reformatted subfolder lists for better readability
pyabc2/sources/bill_black.py	Migrated URLs to HTTPS, changed s-tunes-2 from .txt to .rtf format, added RTF processing logic to strip trailing backslashes and closing braces

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[zmoon]

in RTD, Norbeck zip is now failing to download

ConnectionError: HTTPSConnectionPool(host='www.norbeck.nu', port=443): Max retries exceeded with url: /abc/hn202601.zip (Caused by NewConnectionError("HTTPSConnection(host='www.norbeck.nu', port=443): Failed to establish a new connection: [Errno 101] Network is unreachable"))

though it worked 10 min ago