Add brokered IPv4 TCP clients

[wdcui]

This PR wires IPv4 TCP client sockets through the broker-owned Linux reactor while keeping descriptor flags, blocking behavior, timeouts, polling, and waiters local to LiteBox. It adds operation-scoped shared-buffer transfers, authoritative local-address and socket-error status, Linux-compatible connect/error/half-close/readiness behavior, and explicit handling for advisory TCP options, stream MSG_TRUNC, and unsupported linger. It also adds syscall-rewriter loopback coverage for blocking and nonblocking I/O, backpressure, poll/epoll, shutdown, names, policy denial, refused connections, and resets.

[github-actions]

🤖 SemverChecks 🤖 ⚠️ Potential breaking API changes detected ⚠️

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--- failure enum_discriminants_undefined_non_unit_variant: enum's variants no longer have defined discriminants due to non-unit variant ---

Description:
An enum's variants no longer have well-defined discriminant values due to a tuple or struct variant in the enum. This breaks downstream code that accesses discriminants via a numeric cast like `as isize`.
        ref: https://doc.rust-lang.org/reference/items/enumerations.html#assigning-discriminant-values
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.49.0/src/lints/enum_discriminants_undefined_non_unit_variant.ron

Failed in:
  enum ChannelReadError in /home/runner/work/litebox/litebox/litebox/src/net/socket_channel.rs:136
  enum ChannelWriteError in /home/runner/work/litebox/litebox/litebox/src/net/socket_channel.rs:149

--- failure enum_variant_added: enum variant added on exhaustive enum ---

Description:
A publicly-visible enum without #[non_exhaustive] has a new variant.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#enum-variant-new
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.49.0/src/lints/enum_variant_added.ron

Failed in:
  variant ChannelWriteError:Socket in /home/runner/work/litebox/litebox/litebox/src/net/socket_channel.rs:163
  variant NetworkProxy:BrokerStream in /home/runner/work/litebox/litebox/litebox/src/net/socket_channel.rs:192
  variant ChannelReadError:Socket in /home/runner/work/litebox/litebox/litebox/src/net/socket_channel.rs:144

--- failure enum_missing: pub enum removed or renamed ---

Description:
A publicly-visible enum cannot be imported by its prior path. A `pub use` may have been removed, or the enum 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/v0.49.0/src/lints/enum_missing.ron

Failed in:
  enum litebox_broker_core::socket::SocketOutcome, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/cca158d5641d6abd9e2a9ebf419af5dc9792277a/litebox_broker_core/src/socket.rs:24

--- failure constructible_struct_adds_field: externally-constructible struct adds field ---

Description:
A pub struct constructible with a struct literal has a new pub field. Existing struct literals must be updated to include the new field.
        ref: https://doc.rust-lang.org/reference/expressions/struct-expr.html
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.49.0/src/lints/constructible_struct_adds_field.ron

Failed in:
  field SocketStatusResponse.local_address in /home/runner/work/litebox/litebox/litebox_broker_protocol/src/socket.rs:358
  field SocketStatusResponse.pending_error in /home/runner/work/litebox/litebox/litebox_broker_protocol/src/socket.rs:360