[tlq5l]

Fixes #1106

Cf::request_priority() panicked when requestPriority was an empty string. "".split(';') yields one empty segment, and the parser then called unwrap() on the missing value after splitting on =.

The pairs are now read with split_once('=')?, so an empty string or a segment without key=value returns None. Valid values parse as before. I left the unwrap() on number parsing and the unreachable!() for unknown keys alone (so weight=abc or foo=1 still panic) because the issue does not cover them.

Added wasm tests for the empty string and for a normal value, plus a changeset.

Ran live: cargo test -p worker --target wasm32-unknown-unknown --lib cf:: (wasm-bindgen-test-runner on node) -> the empty-string test panics at cf.rs:86 on the old code and passes with the fix.