feat: update timezone base url

[mitsu-yuki]

Hello! Thank you for this wonderful library!

This PR introduces the following two changes:

1. Update timezone database URL
   The filename of the latest timezone database has been updated to tzdata2025b.tar.gz, so this PR reflects that change.

2. Add the America/Coyhaique timezone
   Following the update in 1., I ran go run scripts/tzgen/main.go to generate the updated timezone data including America/Coyhaique.

For further details on the timezone database updates, please refer to:
https://data.iana.org/time-zones/tzdb/NEWS

[Code-Hex]

Thank you so much!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (692ff06) to head (3f7201f).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

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##              main       #40   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           16        16           
  Lines         2672      2672           
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  Hits          2672      2672           

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