pr: fix combined flags, -s alignment, and -T pagination

[dragutreis]

Fix pr -3Ts, parsing and formatting issues

Fixes #12313

This fixes a few related issues in pr that showed up when using it to transpose columns, for example:

<in.csv tr , \\n | pr -3Ts,

Fixed issues

• -3Ts, was not parsed correctly because the argument rewrite step dropped the trailing flags before clap saw them
• -s still aligned columns with padding spaces.
• -T removed headers/footers but still left page separators between chunks of output

Changes

• Split combined args like -3Ts, into -3 and -Ts, during argument preprocessing
• Disable column alignment when -s is explicitly passed (unless -S is also used)
• Stop writing page separators when -T / --omit-pagination is active
• Fixed an extra blank-line case in write_columns under -T

Note

There’s still a pre-existing issue where pagination boundaries are based on page_length - 10 even with -T, so output still wraps every 56 lines instead of 66. That behavior is unchanged in this PR.