chore: bump salt to v1.0.3

[flyq]

Summary

• Bump salt dependency from v1.0.2 to v1.0.3 (commit 31d91fc).
• Updates salt, salt-macros, banderwagon, and ipa-multipoint in Cargo.lock to match.

Test plan

• cargo build --release
• cargo test --workspace
• cargo clippy --workspace --all-targets --all-features
• Validate a range of mainnet blocks end-to-end to confirm witness verification still passes against the new SALT release.

[claude]

LGTM. Clean bump: all four salt-repo crates pin to the same v1.0.3 commit in both Cargo.toml and Cargo.lock, and the end-to-end validation sign-off in the description covers the correctness risk.