dd: fix various i64 max errors

[zhw2101024]

Fixes #12964
There's some cases on the i64 boundary where uutils dd cannot handle correctly.

[zhw2101024]

Forgot to test on windows, will try again later.

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/dd/misc. tests/dd/misc is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/pr/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tail/symlink (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/cp/link-heap is now passing!

[codspeed-hq]

Merging this PR will not alter performance

✅ 323 untouched benchmarks
⏩ 46 skipped benchmarks¹

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_{Comparing zhw2101024:fix_various_i64_max_errors (9987869) with main (395da6a)}

Footnotes

1. 46 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩