data: Add 2025a

[github-actions]

This contains the following changes from tzdb (edited this to remove details irrelevant to this project):

Release 2025a - 2025-01-15 10:47:24 -0800

  Briefly:
    Paraguay adopts permanent -03 starting spring 2024.
    Improve pre-1991 data for the Philippines.

  Changes to future timestamps

    Paraguay will stop changing its clocks after the spring-forward
    transition on 2024-10-06, so it is now permanently at -03.
    (Thanks to Heitor David Pinto and Even Scharning.)
    This affects timestamps starting 2025-03-22, as well as the
    obsolescent tm_isdst flags starting 2024-10-15.

  Changes to past timestamps

    Correct timestamps for the Philippines before 1900, and from 1937
    through 1990.  (Thanks to P Chan for the heads-up and citations.)
    This includes adjusting local mean time before 1899; fixing
    transitions in September 1899, January 1937, and June 1954; adding
    transitions in December 1941, November 1945, March and September
    1977, and May and July 1990; and removing incorrect transitions in
    March and September 1978.

  Changes to data

    Add zone1970.tab lines for the Concordia and Eyre Bird Observatory
    research stations.  (Thanks to Derick Rethans and Jule Dabars.)

[yakirza17]

@gilmoreorless any update?

[gilmoreorless]

Sorry, I should have posted an update earlier. This PR got blocked by two other tasks:

1. Some data weirdness in the tests that are failing on the main branch but not in this PR.
2. Website documentation regarding a nuance in the data. This particular release contains a change that I'm sure is going to confuse some people.

My time has been quite limited lately, but I finished the docs yesterday, and should be able to merge & release this soon.

[gilmoreorless]

Released in 0.5.47