fix: register @zstd_toolchains//:all

[thesayyn]

I don't know why Bazel did not complain that the toolchain wasn't registered.

Changes are visible to end-users: yes/no

• Searched for relevant documentation and updated as needed: yes
• Breaking change (forces users to change their own code or config): no
• Suggested release notes appear below: no

Test plan

• Covered by existing test cases

[aspect-workflows]

Test

3 test targets passed

Targets

//lib/tests/copy_to_directory_bin_action:test [k8-opt] 69ms
//lib/tests/jq:check_stamped [k8-opt]                  89ms
//lib/tests/yq:check_stamped [k8-opt]                  16ms

Total test execution time was 174ms. 227 tests (98.7%) were fully cached saving 39s.

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Test

e2e/copy_to_directory

All tests were cache hits

6 tests (100.0%) were fully cached saving 660ms.

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Test

e2e/coreutils

All tests were cache hits

4 tests (100.0%) were fully cached saving 578ms.

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Test

e2e/external_copy_to_directory

All tests were cache hits

1 test (100.0%) was fully cached saving 52ms.

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Test

e2e/smoke

All tests were cache hits

6 tests (100.0%) were fully cached saving 1s.

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Buildifier      Format      Gazelle

[thesayyn]

I know why, because we don't have a WORKSPACE.bzlmod file so WORKSPACE gets evaluated alongside bzlmod...