2.1.10 - released 2021-10-29

Changelog

Added type annotations to all classes, which may have an effect on CI/static analysis for people using Composer as a dependency (#10159)
Fixed CurlDownloader requesting gzip encoding even when no gzip support is present (#10153)
Fixed regression in 2.1.6 where the help command was not working for plugin commands (#10147)
Fixed warning showing when an invalid cache dir is configured but unused (#10125)
Fixed require command reverting changes even though dependency resolution succeeded when something fails in scripts for example (#10118)
Fixed require not finding the right package version when some newly required extension is missing from the system (#10167)
Fixed proxied binary file issues, now using output buffering (e1dbd65aff)
Fixed and improved error reporting in several edge cases (#9804, #10136, #10163, #10224, #10209)
Fixed some more Windows CLI parameter escaping edge cases