Fix transport compression feature & add CI tests (#3067) #932

Job	Run time
Test (nightly)	1m 43s
Build docs	44s
Test (stable)	2m 34s
Test (macOS)	1m 25s
Test (beta)	2m 59s
Check minimal versions	28s
Test (Windows)	4m 30s
MSRV	0s
Test (native-tls)	2m 33s
Test (no default features)	50s
Test (no cache)	2m 26s
Test (no gateway)	1m 48s
Test (unstable Discord API features)	2m 51s
Test (zlib compression)	2m 35s
Test (zstd compression)	2m 38s
Test (zlib and zstd compression)	2m 38s
Test (chrono, chrono)	52s
Test (unstable API + typesize, default unstable typesize, true)	1m 4s
Test (builder without model, builder, true)	35s
Test (unstable Discord API (no default features), unstable, true)	34s
Examples	2m 41s
	38m 28s

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