Add AsyncDrainWriter to eliminate PrintWriter lock contention

[gnodet]

Summary

During parallel model building (-T1C), multiple PhasingExecutor threads log concurrently via:

SLF4J → MavenSimpleLogger → ProjectBuildLogAppender → SimpleBuildEventListener → PrintWriter.println()

Since PrintWriter.println() is synchronized, all threads serialize on every log call. JFR profiling on a 4383-module diamond-graph project shows 1,470ms of blocked time from this single contention point — the #1 source of lock contention during validate.

Fix

AsyncDrainWriter wraps the Consumer<String> writer with a lock-free queue + non-blocking drain:

• Producers enqueue messages into a ConcurrentLinkedQueue (CAS, no blocking)
• At most one thread drains the queue to the underlying PrintWriter (via ReentrantLock.tryLock())
• Other threads return immediately after enqueue — their messages are picked up by the active drain
• close() performs a final blocking drain to guarantee no messages are lost

JFR Results (4383-module diamond project, validate -T1C)

Source	Before	After
PrintWriter contention	1,470ms	0ms
PhasingExecutor contention	546ms	49ms

Benchmark (10 runs)

Metric	Before	After	Δ
Median	14.738s	14.253s	-485ms (-3.3%)
Average	14.546s	14.242s	-304ms (-2.1%)
Range (variance)	2.70s	1.33s	Halved

All 8,766 module log lines verified present — zero messages lost.

Test plan

• Verified 8,766/8,766 module log lines present (no lost messages)
• JFR confirms PrintWriter contention eliminated (1,470ms → 0ms)
• maven-core unit tests pass
• maven-cli unit tests pass
• CI passes

🤖 Generated with Claude Code