feat(datagen): add IPv6 to NetworkIdentity and public emission (PIPE-1001)

[Dylan-M]

Stacked on #274

Proposed Change

Adds IPv6 to datagen's network model, which was IPv4-only.

• NetworkIdentity gains an IPv6CIDR field, GenerateDefaultNetworks emits
  dual-stack defaults, and Validate() applies per-family prefix floors.
• RandomPublicIPv6 generates a global-unicast (2000::/3) address and rejects
  reserved-block hits; RandomIPInCIDRv6 is the IPv6 counterpart of
  RandomIPInCIDR.
• Populates reservedIPv6Blocks with RFC-attributed entries (RFC 4291
  unspecified / loopback / IPv4-mapped / link-local / multicast, RFC 4193
  unique-local, RFC 3849 documentation, and the rest).
• Splits ValidateCIDR into IPv4 and IPv6 validation.

Address generation only; no routing or protocol simulation.

Validation: generate a batch of public IPv6 addresses and confirm none land in a
reserved block. Tests cover dual-stack defaults, per-family floors, reserved-block
rejection during public emission, and in-CIDR generation.

Checklist

• Changes are tested
• CI has passed

[Dylan-M]

Warning

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Learn more

• feat(config): reject invalid network CIDRs at environment load (PIPE-1002) #281
• feat(generators): emit simulated host identity on every record (PIPE-1036) #280
• feat(resource): support list-valued resource attributes (PIPE-1253) #279
• feat(datagen): environment foundations for simulated host identity (PIPE-1036) #278
• refactor(datagen): thread an injected logger, drop global-logger use (PIPE-1067) #277
• fix(datagen): return errors instead of panicking on developer-error input (PIPE-1003) #276
• feat(datagen): add IPv6 to NetworkIdentity and public emission (PIPE-1001) #275 👈 (View in Graphite)
• feat(datagen): add storage, network, and appliance-OS identities (PIPE-1035) #274
• main

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