Harden decoder and refresh CI

[casperbiering]

Summary

• harden binary decoder reads and use explicit little-endian helpers
• fix signed Int64 decoding and TimeSpan fractional formatting
• remove XMLReader error suppression and restore libxml state
• refresh Composer scripts/autoload, CI matrix, README badge, and add .editorconfig

Tests

• composer validate --strict --no-check-publish
• composer lint
• composer test