[slachiewicz]

Flyweight var data can be read only as a new string (<Name>(), Get<Name>AsString()), which allocates, or copied into a caller's buffer (Get<Name>(dst)). This adds <Name>Bytes() []byte, which returns the data as a slice of the message buffer, capacity capped at its length, and moves past it like the other getters. The slice is valid only while the buffer holds the message, as the generated comment says. A field added in a later version returns nil for an older message.

It also adds BenchmarkEncodeCar, BenchmarkDecodeCar and BenchmarkDecodeCarBytes to the flyweight baseline package; the decode benchmarks read every field of the Car, groups included, with the four var data fields read as strings or as bytes. Linux arm64 (Azure Cobalt 100), Go 1.27, alternating, 10 runs each:

	ns/op	allocs/op
BenchmarkDecodeCar (var data as strings)	176.53	6
BenchmarkDecodeCarBytes (var data as bytes)	89.62	0

Reading a single 52-byte var data field of an Aeron Archive ReplayRequest: <Name>() 34.88 ns and 1 allocation, Get<Name>(dst) 13.88 ns, <Name>Bytes() 11.64 ns and no allocation.

Verified: ./gradlew generateGolangCodecs && cd gocode && make → all Go tests pass, including the new TestVarDataBytes (values, aliasing of the message buffer, capped capacity, no allocations); a schema with sinceVersion="1" var data returns the value at version 1 and nil at version 0; checkstyle clean.