Add a `--platform` argument to enable resolving against a target platform #5202

Job	Run time
cargo test \| windows	4m 35s
cargo fmt	26s
build binary \| macos aarch64	1m 3s
cargo clippy \| ubuntu	43s
build binary \| linux	1m 13s
cargo clippy \| windows	3m 38s
cargo test \| ubuntu	3m 45s
check windows trampoline	3m 22s
cargo test \| macos	3m 54s
build binary \| macos x86_64	1m 40s
build binary \| windows	4m 15s
check system \| python on macos aarch64	14s
check system \| homebrew python on macos aarch64	17s
check cache \| macos aarch64	11s
check cache \| ubuntu	46s
check system \| python on fedora	34s
check system \| python on debian	42s
ecosystem test \| prefecthq/prefect	1m 48s
check system \| python on opensuse	33s
check system \| pypy on ubuntu	24s
ecosystem test \| pallets/flask	13s
check system \| python on rocky linux	1m 9s
check system \| python on ubuntu	25s
check system \| alpine	23s
check system \| amazonlinux	26s
check system \| python via pyenv	1m 41s
check system \| pyston	3m 47s
check system \| python on macos x86_64	47s
check system \| python3.10 on windows	55s
check system \| python3.12 via chocolatey	1m 34s
check system \| python3.13 on windows	1m 12s
check system \| conda3.8 on linux	40s
check system \| python3.10 on windows x86	54s
check system \| conda3.11 on linux	47s
check system \| conda3.8 on windows	1m 52s
check system \| conda3.11 on windows	2m 16s
check system \| conda3.8 on macos	54s
check system \| conda3.11 on macos	41s
	54m 39s

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