feat(network): add isolated packet codec and stream layer

[wtbdev]

Summary

• add the isolated Packet frame codec and protocol packet types
• add game stream and GZIP block reader/writer layers under network.io
• add codec and stream unit tests

Compatibility

• the default outer packet length limit remains disabled; negative lengths are still rejected
• this PR does not depend on game-lib.jar or deobfuscation mappings
• the existing runtime entry points are not switched in this PR

Verification

• bash gradlew --no-daemon test