test(cli): run fetch and completion operations on paused time

[kixelated]

Problem

Fetch and completion tests race short wall-clock budgets against real connection setup and packet delivery under host load.

Approach

Privately separate fetch setup from its operation and supply an in-memory origin to completion requests. Run operation tests on paused time while retaining separate real dialing and HTTP parity coverage. Fetch still uses one absolute 30 s deadline for setup, discovery, and every read.

Impact

• Public API: none; all new seams are private to the CLI.
• Wire and CLI behavior: unchanged.
• Completed /quest/m1/test-flakes-2/cli-paused-clock.md.

Alternatives

An exported test-support transport API would require new public surface. Local origins reuse the existing model and keep this change confined to the CLI.

Validation

• All 20 fetch/completion tests pass, including blocked setup and setup consuming half the shared deadline.
• Resetting the deadline after setup fails the new regression: 45 simulated seconds versus 30.
• just check and quest check pass; the check covers 125 default-feature tests and 136 with play.
• Inline tests remain in the existing default-feature nextest CI gate.

Follow-ups

None required. Leave this child draft for the questline's review and merge decision.

(Written by GPT-6)

[kixelated]

Merge summary:

• Fetch and completion operation tests now run on paused time against an in-memory origin; real dialing and HTTP /fetch parity coverage is kept separately. Fetch keeps one absolute 30 s deadline across setup and reads.
• Public API and wire: none (private CLI seams only).
• Completes /quest/m1/test-flakes-2/cli-paused-clock.md and removes it from the questline's Required.
• CI green, clean against quest/m1/test-flakes-2/README. No reviews; merge approved by the maintainer.
• Heads-up: rs/moq-cli/src/fetch.rs will conflict when the questline next merges main (feat(cli)!: inspect a relay with moq ls and moq fetch #4032 and feat!: rename announce events to Start/Update/End/Live #4384 changed it).

Enabling auto-merge (merge commit, matching prior questline children).

(Written by Claude Opus 5.5)