P2 download race condition

[nedtwigg]

When used in a Spotless build, it is sometimes triggering this race condition:

Caused by: java.lang.RuntimeException: java.nio.file.FileAlreadyExistsException: /home/jenkins/.m2/repository/dev/equo/p2-data/bundle-pool/https-eclipse-p2-mirror.com-p2-4.34-/com.sun.jna_5.15.0.v20240915-2000.jar
	at dev.equo.solstice.p2.Unchecked.wrap(Unchecked.java:25)
	at dev.equo.solstice.p2.P2QueryResult.<init>(P2QueryResult.java:38)
	at dev.equo.solstice.p2.P2Model.query(P2Model.java:137)
	at com.diffplug.spotless.extra.EquoBasedStepBuilder.lambda$build$0(EquoBasedStepBuilder.java:128)
	... 82 more
Caused by: java.nio.file.FileAlreadyExistsException: /home/jenkins/.m2/repository/dev/equo/p2-data/bundle-pool/https-eclipse-p2-mirror.com-p2-4.34-/com.sun.jna_5.15.0.v20240915-2000.jar
	at dev.equo.solstice.p2.JarCache.download(JarCache.java:65)
	at dev.equo.solstice.p2.P2Client.download(P2Client.java:76)
	at dev.equo.solstice.p2.P2QueryResult.<init>(P2QueryResult.java:35)
	... 84 more