What is the purpose of the change?

Fixes #16520

UnsafeByteArrayInputStream.skip(long) can overflow its mPosition + len bounds check for a large positive count after the cursor has advanced. For example, after reading one byte of a slice, skip(Long.MAX_VALUE) reports Long.MAX_VALUE rather than the remaining byte count and can move the cursor backwards. The same request at EOF can make already-consumed bytes readable again.

Compare the requested count with the remaining bytes before updating the cursor. This keeps skipping bounded to the current slice and preserves zero/negative skips, EOF, and mark/reset behavior.

Regression coverage includes Long.MAX_VALUE, Long.MAX_VALUE - 1, a large non-overflowing control, a nonzero slice offset, EOF, mark/reset, and nonpositive counts. Three regression invocations fail against the unmodified source and pass with the fix.

Validation on OpenJDK 21 (the project compiles with release 8): all 13 UnsafeByteArrayInputStreamTest invocations and all 48 I/O-package tests pass, with no failures, errors or skips. The Maven lifecycle Spotless check and git diff --check pass. This is focused module verification; full-repository and production-network testing were not run.

Validation checklist

• Linked reproducible GitHub issue.
• Description explains the trigger, expected behavior and minimal fix.
• Regression tests executed locally; failures reproduced before the change.
• GitHub Actions: pending the newly submitted PR.

Investigation and patch preparation were AI-assisted; the stated local tests were actually executed.