feat: honor `http_proxy` environment variables #1917

Job	Run time
Xcode Build for iOS	50s
Xcode Build for iOS	50s
Lint	19s
Lint	19s
Linux (GCC 7, 32-bit)	1m 39s
Linux (GCC 7, 32-bit)	1m 39s
Linux (GCC 9.4.0)	8m 42s
Linux (GCC 9.4.0)	8m 42s
Linux (GCC 12)	9m 3s
Linux (GCC 12)	9m 3s
Linux (clang 15 + asan + llvm-cov)	9m 54s
Linux (clang 15 + asan + llvm-cov)	9m 54s
Linux (clang 15 + kcov)	30m 34s
Linux (clang 15 + kcov)	30m 34s
Linux (gcc 12 + code-checker + valgrind)	8m 59s
Linux (gcc 12 + code-checker + valgrind)	8m 59s
macOS 14 (xcode llvm)	9m 29s
macOS 14 (xcode llvm)	9m 29s
macOS 13 (xcode llvm)	8m 48s
macOS 13 (xcode llvm)	8m 48s
macOS 14 (xcode llvm + universal)	7m 55s
macOS 14 (xcode llvm + universal)	7m 55s
macOS 15 (clang 18 + asan + llvm-cov)	13m 58s
macOS 15 (clang 18 + asan + llvm-cov)	13m 58s
Windows (old VS, 32-bit)	12m 53s
Windows (old VS, 32-bit)	12m 53s
Windows (latest)	9m 57s
Windows (latest)	10m 59s
LLVM-Mingw	17m 7s
LLVM-Mingw	17m 7s
Android (API 35, NDK 27)	4m 21s
Android (API 35, NDK 27)	4m 21s
Create Release Archive	0s
Create Release Archive	0s
	5h 9m 58s

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