This sounds great, but the "accounting" in your example looks like a hassle. Maybe there's a good way to do the following (pseudocode):

use Test::More tests => 25;  # 25 unconditionally

...

ADDITIONAL: {
  skip "Skipping additional tests; try ENV{ALL_TESTS}\n", ADDITIONAL
    unless $ENV{ALL_TESTS};
  
  $Test::More::tests += 95;
  # 95 more tests here ...
}
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