Add unit tests for `StreamPeerTCP` #69523

Job	Run time
📊 Static checks / Code style, file formatting, and docs	1m 51s
🤖 Android / Template arm64 (target=template_release, arch=arm64)	4m 2s
🤖 Android / Editor (target=editor)	24m 26s
🍏 iOS / Template (target=template_release)	2m 8s
🤖 Android / Template arm32 (target=template_release, arch=arm32)	5m 2s
🍎 macOS / Template (target=template_release)	4m 44s
🍎 macOS / Editor (target=editor)	31m 53s
🐧 Linux / Editor w/ Mono (target=editor)	41m 13s
🐧 Linux / Template w/ Mono, release (target=template_release)	9m 8s
🐧 Linux / Editor with doubles and GCC sanitizers (target=editor, dev_build=yes, scu_build=yes, precision=double, use_asan=yes, use_ubsan=yes, linker=mold)	49m 18s
🐧 Linux / Template w/ Mono, debug (target=template_debug)	9m 55s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	3m 50s
🐧 Linux / Editor with ThreadSanitizer (target=editor, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	12m 7s
🐧 Linux / Editor with clang sanitizers (target=editor, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	30m 45s
🏁 Windows / Editor w/ clang-cl (target=editor, use_llvm=yes)	21m 14s
🏁 Windows / Editor (target=editor)	40m 8s
🏁 Windows / Template w/ GCC (target=template_release, use_mingw=yes)	28m 19s
🌐 Web / Template w/o threads (target=template_release, threads=no)	4m 18s
🏁 Windows / Template (target=template_release)	6m 12s
🐧 Linux / Minimal template (target=template_release, everything disabled)	5m 56s
	5h 36m 29s

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