Fix incorrect Facts in pkl:base doc comments

[adityasingh2400]

Several Facts: examples in the pkl:base standard library docs assert statements that are false when evaluated. Since these examples are not run by any test, the mistakes went unnoticed and are rendered verbatim into the generated API docs, where they mislead readers.

The corrected examples:

• String.isNotBlank: "\t\n\r".isNotBlank was listed as holding, but a string of only whitespace is blank, so it is false. Negated it to match the neighboring !"".isNotBlank and !" ".isNotBlank examples.
• DataSize.toBinaryUnit / toDecimalUnit: the mb/mib lines mirrored the kb/kib lines, but the identity only holds for adjacent units. 1024.kb == 1000.kib (both 1,024,000 b), whereas 1024.mb is 1,024,000,000 b and 1000.mib is 1,048,576,000 b, so they are not equal. There is no clean round-number equivalent at this magnitude, so I removed the two false lines; the remaining examples still demonstrate the conversion.
• Collection.any: !List(1, 2, 3).any((n) -> n.isEven) is false because 2 is even. Changed the list to List(1, 3, 5) so the negation holds.
• IntSeq.end: the example read IntSeq(2, 5).start == 5, which documents the wrong property and is false (start is 2). Corrected it to IntSeq(2, 5).end == 5.
• List.isDistinctBy / distinctBy: List("a", "b", "abc") is not distinct by length, since "a" and "b" both have length 1. Switched to List("a", "bb", "ccc") so the distinctness examples hold.
• Map: Map(...).values returns a List, not a Set. Corrected the expected type.

I verified that each corrected example evaluates to true, and that the neighboring examples I kept still pass, using the released Pkl 0.31.1 binary. The changes are confined to doc-comment text, so formatting is unaffected.

This reopens #1615, which I had withdrawn, at @bioball's suggestion. The fork backing that PR was deleted in the meantime, so GitHub would not let me reopen it directly. This branch carries the exact same change.

[bioball]

LGTM, thank you!

[bioball]

@adityasingh2400 run OVERWRITE_SNIPPETS=1 ./gradlew pkl-core:check to overwrite the snippet tests

[adityasingh2400]

Thanks for the review and the approve. I ran OVERWRITE_SNIPPETS=1 ./gradlew pkl-core:check and it regenerated the reflectedDeclaration snippet for the corrected isNotBlank fact. Pushed the updated expectations just now.

[bioball]

Thanks for fixing these!