release: prepare 0.5.4

[FunKite]

Summary

• bump OctaIndex3D to 0.5.4
• update README and changelog for the 0.5.4 release
• stop tag-triggered CI from publishing to crates.io; keep tag-triggered GitHub Release creation only
• fix ESDF all-features validation by deduplicating the frontier queue and bounding the unit test fixture

Validation

• ./scripts/safe_local_test.sh
• cargo test --all-features
• cargo publish --dry-run
• cargo publish

Release

• published octaindex3d 0.5.4 to crates.io
• pushed tag v0.5.4
• GitHub Release v0.5.4 created successfully