feat: memory-only mode skips the timed rounds (closes #124)

[FBumann]

Closes #124.

Problem

A capacity benchmark marked @pytest.mark.benchmem(isolate=True) only wants rss, but pytest-benchmark still runs its full timed rounds. When the payload rebuilds heavy state every round (the linopy LP-writer sweep in the issue: ~79 s/case, almost all of it discarded timing), that's pure overhead.

Solution

A memory-only mode that runs the memray pass as usual, then a single timed call — the timing column shows that one call's duration — instead of the full rounds:

@pytest.mark.benchmem(isolate=True, time=False)
def test_whole_pipeline(benchmark_memory):
    benchmark_memory(build_and_write, spec, n)   # rss measured; one timed call, not N rounds

• marker: time=False (per-test)
• suite-wide: --benchmark-memory-only (a per-test time=True opts back in)

Both entry points honour it — the benchmark_memory fixture and the --benchmark-memory monkeypatch — by routing the timed leg through pedantic(rounds=1, warmup_rounds=0, iterations=1). The memory pass (repeats / isolate / ceilings) is untouched.

Design notes

• Resolver mirrors the existing marker+global blend used by profile_native (_memory_only_from_node / _global_memory_only).
• Truly dropping timing (—) isn't clean — pytest-benchmark needs a stats entry to emit the row and carry the memory blob — so "exactly one round" is the realistic form, as flagged on the issue.
• Reference marker table gains a time row + an isolate-path tip; the live flags table picks up --benchmark-memory-only automatically.

Tests

time=False collapses to one round while leaving the memory blob and unmarked tests intact; --benchmark-memory-only collapses all; time=True overrides the flag; and the --benchmark-memory patch path honours time=False. Full suite green; ruff + format + mypy clean.

🤖 Generated with Claude Code

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