fix(paroche): encode kosync sha1 hashes explicitly

[forkwright]

Summary

• replace sha1 0.11 {:x} formatting with an explicit lowercase hex encoder
• keep the KOSync create-user request private and skip request capture in tracing
• reuse the same hash helper in KOSync route tests

Unblocks #236 / #235 by fixing the mainline paroche compile failure.

Validation

• cargo +1.94 fmt --check
• CARGO_TARGET_DIR=/data/target/wt/paroche-sha1-hex/target cargo +1.94 check -p paroche
• CARGO_TARGET_DIR=/data/target/wt/paroche-sha1-hex/target cargo +1.94 test -p paroche kosync
• CARGO_TARGET_DIR=/data/target/wt/paroche-sha1-hex/target cargo +1.94 clippy -p paroche -- -D warnings
• RUST_LOG=error kanon lint --rust --summary crates/paroche/src/routes/kosync.rs
• git diff --check