Merge upstream/main (59cf8189) into submodule/base

Sync the base fork with 13 upstream commits (xhci event-processing
dedup + IRQ race fix, randd permission simplification, nvmed TimeSpec
fix, /dev/ptmx, fpath legacy-path cleanup, dynamically-linked init
fix, and more). Brings process_one_event into the tree, satisfying the
verify-fork-functions gate for base.

Conflicts resolved (3 of 8 overlapping files; 5 auto-merged):

- drivers/usb/xhcid/src/xhci/irq_reactor.rs: took upstream's
  process_one_event/EventProcessResult refactor (b2ed85ea) including
  the a01d3ce6 race fix (process events between NoEvent and
  unmasking), and re-applied the Red Bear SPURIOUS_REBOOT quirk on the
  NoEvent warning (downgrade to debug when quirked).

- randd/src/main.rs: took upstream's permission-handling
  simplification (e26db606); re-applied the RB fcntl improvement
  (F_GETFL/F_GETFD/F_SETFL/F_SETFD handling, Linux random_fops xref)
  and the is_cpu_feature_detected early-return cleanup. Dropped
  test_scheme_perms (deleted by upstream's simplification).

- Makefile: kept upstream's new /dev symlink block (dev/null, ptmx,
  random, urandom, zero, tty, stdin/stdout/stderr).

Verified: cargo check clean; 57/57 tests pass (xhcid 35, usbhubd 14,
xhci trb 8); verify-fork-functions.sh --no-fetch base reports all
upstream functions present.

scheme-utils/src/lib.rs

@@ -92,17 +92,6 @@ impl<'a> FpathWriter<'a> {
         Ok(w.written)
     }
 
-    pub fn with_legacy(
-        buf: &'a mut [u8],
-        scheme_name: &str,
-        f: impl FnOnce(&mut Self) -> Result<()>,
-    ) -> Result<usize> {
-        let mut w = FpathWriter { buf, written: 0 };
-        write!(w, "{scheme_name}:").unwrap();
-        f(&mut w)?;
-        Ok(w.written)
-    }
-
     pub fn push_str(&mut self, s: &str) {
         let count = core::cmp::min(s.len(), self.buf.len() - self.written);
         self.buf[self.written..self.written + count].copy_from_slice(&s.as_bytes()[..count]);