Fast test/surfaces-adversarial.test.ts: chop and rewrite under the budget (1 s a test, 10 s a file) #12064

test/surfaces-adversarial.test.ts is now under the budget: its slowest test went from about 1.0 s to 0.47 s here, and the other N+1 tests dropped from about 0.7 s to 0.27–0.38 s. All 13 tests pass and bun x tsc --noEmit is clean. bun scripts/gate.ts printed nothing. I did not read scripts/test-times.json after the change, so the gate's file total is not confirmed.

• Where the time went: each N+1 test hashed passwords with argon2 for the users it created and again when signing them in. The statements helper then measured five times per count, waiting for quiet each time.
• What changed: the N+1 tests now create passwordless seeded users and sign them in with a session row via createSession, so nothing is hashed. They measure twice per count instead of five times. The helper itself is untouched. Two runs still catch a real N+1, because that costs more in every run.
• Invariant lines: each of the five N+1 tests now has its invariant written as a one-line comment at the top.
• Removed: the unused signUp and loginAs helpers, and the stray signUp call that was only there to reuse a cookie shape.
• Not done: no test was deleted, since each proves a different listing's query count. I did not split the file or move anything to NIGHTLY. The issue says the file has a SLOW entry in scripts/gate.ts, but none exists on this branch, so there was nothing to remove. I did not change the gate.
• To try: bun test test/surfaces-adversarial.test.ts.

Closes #1338

test/surfaces-adversarial.test.ts is now under the budget: its slowest test went from about 1.0 s to 0.47 s here, and the other N+1 tests dropped from about 0.7 s to 0.27–0.38 s. All 13 tests pass and bun x tsc --noEmit is clean. bun scripts/gate.ts printed nothing. I did not read scripts/test-times.json after the change, so the gate's file total is not confirmed.

• Where the time went: each N+1 test hashed passwords with argon2 for the users it created and again when signing them in. The statements helper then measured five times per count, waiting for quiet each time.
• What changed: the N+1 tests now create passwordless seeded users and sign them in with a session row via createSession, so nothing is hashed. They measure twice per count instead of five times. The helper itself is untouched. Two runs still catch a real N+1, because that costs more in every run.
• Invariant lines: each of the five N+1 tests now has its invariant written as a one-line comment at the top.
• Removed: the unused signUp and loginAs helpers, and the stray signUp call that was only there to reuse a cookie shape.
• Not done: no test was deleted, since each proves a different listing's query count. I did not split the file or move anything to NIGHTLY. The issue says the file has a SLOW entry in scripts/gate.ts, but none exists on this branch, so there was nothing to remove. I did not change the gate.
• To try: bun test test/surfaces-adversarial.test.ts.