fix(raw): reject dot-dot segments revealed by decoding encoded separators

rejectPathTraversal split components on literal "/" before checking
each segment, so a segment containing an encoded separator (e.g.
"%2e%2e%2fsecret.txt") decoded to "../secret.txt" instead of "..", and
the check never caught it. Percent-decoding a segment can therefore
introduce new "/"-separated subsegments that were invisible to the
original literal split.

Recursively re-split and re-check the decoded form whenever decoding
changes a segment, so a ".." revealed by one or more layers of
percent-decoding (including through an encoded separator, or
double-encoding) is rejected regardless of where it appears.

Add regression tests for encoded-separator traversal, encoded
separators in other components, and double percent-encoded dot-dot
segments, plus a benign percent-encoded filename case to confirm
non-traversal decodes still pass through.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>