pr: allow character, block, and fifo devices as input

[SaathwikDasari]

Fixes #9935

Problem: Running pr on character devices (e.g., /dev/zero) or FIFOs triggers an unknown filetype error because the check was limited to regular files and symlinks.

Solution: Updated the match logic in src/uu/pr/src/pr.rs to accept is_char_device(), is_block_device(), and is_fifo() as valid inputs, matching GNU pr behavior.

Testing:

Manual: cargo run --bin coreutils -- pr /dev/zero now reads the stream instead of erroring.
cargo test --package uu_pr passed.

Style: Ran cargo fmt.

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/tty/tty-eof. tests/tty/tty-eof is passing on 'main'. Maybe you have to rebase?

[SaathwikDasari]

All core logic is complete and I have verified the fix for /dev/zero locally.

I have also addressed the unused-mut warning for Windows to ensure cross-platform compatibility. Regarding the remaining CI failures:

1. The Style/format failure was a network timeout during the 'Set up job' phase (fetching the toolchain).

2. The tty-eof failure appears to be a known flaky test unrelated to the changes in pr.rs.

This PR is ready for review.

[sylvestre]

please add a test to cover this change

[sylvestre]

Suggested change

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[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)