[Logic769]

Problem

split -n +2 file fails with "invalid number of chunks" because the leading + is not stripped before parsing, whereas GNU split accepts it.

Change

In NumberType::from, strip an optional leading + before parsing the chunk count.

Tests

Added test_number_with_plus_prefix in tests/by-util/test_split.rs, checking that -n +2 splits the file into two chunks.

Closes #16006

[Logic769]

Pulled the + out in a helper before parse_size_u64 so every K/N is covered, and added l/+2 with content checks and r/+1/2.

[sylvestre]

a bunch of jobs are failing