Add shared guest IPv4 identity

[Weidong Cui (wdcui)]

This PR adds the fixed shared guest IPv4 identity 10.0.2.15 to the existing broker-wide TCP and UDP namespaces, simplifies socket policy into independent per-protocol settings, supports exact and wildcard guest bindings with destination-correct source addresses, and makes unmatched private guest destinations fail closed without changing native endpoint lifecycle or gateway routing.

[github-actions]

🤖 SemverChecks 🤖 ⚠️ Potential breaking API changes detected ⚠️

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--- failure enum_changed_kind: pub enum changed kind ---

Description:
A public enum has been replaced by a different kind of item at the same path, which breaks code that relied on the enum's variants and representation.
        ref: https://github.com/obi1kenobi/cargo-semver-checks/issues/302
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/enum_changed_kind.ron

Failed in:
  enum litebox_broker_core::SocketPolicy became struct in /home/runner/work/litebox/litebox/litebox_broker_core/src/policy.rs:203

--- failure inherent_method_missing: pub method removed or renamed ---

Description:
A publicly-visible method or associated fn is no longer available under its prior name. It may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/inherent_method_missing.ron

Failed in:
  SocketPolicy::from_tcp_destination_rules, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/2e2200484433d69afbe19fe0f944c7bebd727b1a/litebox_broker_core/src/policy.rs:228
  SocketPolicy::from_udp_destination_rules, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/2e2200484433d69afbe19fe0f944c7bebd727b1a/litebox_broker_core/src/policy.rs:235
  SocketPolicy::from_tcp_udp_destination_rules, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/2e2200484433d69afbe19fe0f944c7bebd727b1a/litebox_broker_core/src/policy.rs:243

--- failure struct_missing: pub struct removed or renamed ---

Description:
A publicly-visible struct cannot be imported by its prior path. A `pub use` may have been removed, or the struct itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/struct_missing.ron

Failed in:
  struct litebox_broker_core::DestinationPolicy, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/2e2200484433d69afbe19fe0f944c7bebd727b1a/litebox_broker_core/src/policy.rs:177