chore(contracts): enforce fmt + clippy CI gate and clear all lint/format lapses

[EmeditWeb]

Summary

Contracts CI ran only build + test — nothing guarded formatting or lints. Over time 91 rustfmt hunks and 27 clippy warnings accumulated across all six contracts. This PR adds the missing gates and clears the tree, so every future PR is held to the same bar.

What changed

CI gate (.github/workflows/contracts-ci.yml)

• cargo fmt --all --check — fast fail, before any compile.
• cargo clippy --workspace --all-targets -- -D warnings — placed after the dependency-WASM build so creditline's contractimport! clients resolve during the native clippy compile (otherwise E0599 on receive_guarantee).
• Install rustfmt + clippy toolchain components.

Formatting

• rustfmt applied across all six contracts.

Lint fixes (27 → 0)

• assert_eq!(x, <bool>) → assert! in liquidity-pool + creditline tests (10).
• checked_add(..).unwrap_or(u64::MAX) → saturating_add in vouching TTL math — behaviour-identical (2).
• match-to-bool → matches! in creditline reputation-call handling (2).
• Removed unused imports / mut / binding, added an elided lifetime, fixed a rustdoc list indentation.
• Removed the dead safe_math modules from parameters and vendor-registry — both already perform overflow-checked arithmetic inline, so no safety is lost. creditline, liquidity-pool and reputation keep their used copies.
• Removed an unused assert_event test helper.

Test quality

• Added the missing share_price_before == 10_000 baseline assertion in the creditline default-loss test (the value was captured but never asserted — the share_price_after == 9_454 check had no documented starting point).

Verification

Gate	Result
cargo fmt --all --check	clean
cargo clippy --workspace --all-targets -- -D warnings	clean
cargo build --locked --target wasm32-unknown-unknown --release	all six contracts
cargo test --locked	420 passed, 0 failed

Notes

• No behaviour changes to on-chain logic — changes are lint/format/test-only plus the CI gate. The saturating_add and matches! rewrites are exact-equivalent transformations.