macOS /usr/bin/patch cause obscure failures and stalls

[marc-hb]

macOS' /usr/bin/patch and GNU patch have very subtle incompatibilities that cause only some "more advanced" tests to fail in obscure and very time-consuming ways - while other tests pass. In some cases (depending on test threads racing), the lack of newlines in some test data even causes the whole test suite to stall.

failures:
    context_diff::tests::test_permutations
    context_diff::tests::test_permutations_empty_lines
    context_diff::tests::test_permutations_reverse
    unified_diff::tests::test_permutations
    unified_diff::tests::test_permutations_empty_lines
    unified_diff::tests::test_permutations_missing_line_ending
    unified_diff::tests::test_permutations_reverse

test result: FAILED. 118 passed; 7 failed; 0 ignored; 0 measured; 0 filtered out; finished in 13.50s

Examples:

diff: "--- target/unified-diff//alef\t2026-05-06 17:34:45.259112903 -0400\n+++ target/unified-diff//alef\t2026-05-06 17:34:45.259112903 -0400\n@@ -1,4 +1,4 @@\n-a\n-c\n+b\n+d\n f\n h\n@@ -5,2 +5,2 @@\n-i\n+j\n l\n"
alef: "a\nc\nf\nh\ni\nl\n"
bet: "b\nd\nf\nh\nj\nl\n"
patching file 'target/unified-diff//alef'
1 out of 2 hunks failed--saving rejects to 'target/unified-diff//alef.rej'

---- context_diff::tests::test_permutations_reverse stdout ----

thread 'context_diff::tests::test_permutations_reverse' (14471508) panicked at src/context_diff.rs:718:33:
assertion failed: `(left == right)`

Diff < left / right > :
 [
     98,
     10,
<    100,
<    10,
<    99,
<    10,
<    98,
<    10,
<    97,
<    10,
 ]