Fix tsindex feb2024

[chad-earthscope]

What does this PR do?

Changses to the obspy.clients.filesystem.tsindex module:

• More fixes to sqlalchemy 2.x warnings-turned-errors, in particular the need to use sa.text() for PRAGMA statements
• Remove leap second file handling, unnecessary with current mseedindex
• Fix tests for mseedindex >= 3.0.4 and remove leap second related tests
• Rebrand IRIS -> EarthScope and fix URLs

Why was it initiated? Any relevant Issues?

SQLAlchemy failures during testing and new mseedindex program that handles multiple versions of miniSEED.
Note: the mseedindex package in PyPI is now up to date with the current release: https://pypi.org/project/mseedindex/ and likely how ObsPy users will get this program.

PR Checklist

• Correct base branch selected? is now installable via PyPI: master for new features, maintenance_... for bug fixes
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[megies]

@chad-earthscope I think this is mixing changes that can go into maintenance_1.4.x..

• rebranding
• test fixes

.. with a change that should go into master instead:

• functionality change, removing the leap second handling

Can we split this up?

(I changed the merge target branch to see what is actually going on in here)

[megies]

This part is different on the maintenance_1.4.x branch, so not sure what needs to be done exactly if it should go into 1.4.1

[megies]

Same here..

[megies]

Besides these two parts above, the rest could be cherry-picked cleanly on top of a branch off of maintenance_1.4.x