Vendor apple/containerization with a VM-extensions forwarding patch

Switch the containerization dependency from the github URL to a vendored copy
(third_party/containerization, upstream commit 6b7b42ca) referenced by path, so
we can carry a small local patch that upstream lacks: LinuxContainer.Configuration
gains a `vmExtensions` field forwarded into VMConfiguration.extensions. Upstream
already supports VMConfiguration.extensions + the VZInstanceExtension hook, but
LinuxContainer — our only entry point — never forwarded them, so there was no way
to attach a device (e.g. a memory balloon) to a container's VM.

Tests/, docs/, examples/, images/ and the corresponding test targets are trimmed
for footprint (we never build the dependency's tests). See PATCHES.md for the full
diff vs. upstream and the re-vendoring procedure. Also adds the ContainerizationExtras
product to NucleicCore (AddressAllocator, named in the configureVZ signature).

Co-Authored-By: Claude Opus 4.8 <[email protected]>

scripts/license-header.txt

@@ -0,0 +1,13 @@
+Copyright ©{{ " " }}{%- set created = attrs.git_file_created_year or attrs.disk_file_created_year -%}{%- set modified = attrs.git_file_modified_year or created -%}{%- if created != modified -%} {{created}}-{{modified}}{%- else -%}{{created}}{%- endif -%}{{ " " }}{{ props["copyrightOwner"] }}.
+
+Licensed under the Apache License, Version 2.0 (the "License");
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+You may obtain a copy of the License at
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