Make Consomme TCP validation deterministic

Tracking issue: MicroVM support and private snapshot restore.

Motivation

Networking identity, admission limits, and snapshot reconstruction need tests that
can distinguish a protocol regression from host scheduling or timing variation.
Deterministic Consomme TCP fixtures would make those changes easier to review and
keep failure diagnostics reproducible across Windows and Linux.

Proposed Scope

• Drive TCP test inputs, event ordering, and timeout progression explicitly where
  the test harness permits it.
• Remove reliance on incidental wall-clock timing or external network services
  from the targeted fixtures.
• Assert observable protocol transitions and emitted packets instead of only
  checking that a test finishes.
• Keep fixture changes separate from new networking policies or runtime features.

Acceptance Criteria

• Repeated runs produce the same protocol observations for the same input.
• Focused coverage exercises connection establishment, data transfer, and
  termination, including the targeted timeout or failure paths.
• Tests do not require access to an external network service or sleeps chosen
  to mask races.
• The targeted suite passes on Windows and Linux, with useful diagnostics for
  unexpected packets or state transitions.
• Production TCP semantics are unchanged by the fixture work.

Dependencies

No feature prerequisites. These fixtures support later Consomme identity and
resource-admission tests.

Non-Goals

Static addressing, egress policy, flow limits, and network snapshot persistence
are separate issues.