[improve][build] Upgrade lightproto to 0.8.1

[merlimat]

Motivation

Supersedes #26256, which bumped LightProto to 0.8.0 and failed CI: ProxyPatternConsumerBackPressureMultipleConsumersTest ran out of heap. That exposed two regressions in the 0.8.0 generated code, both fixed in LightProto v0.8.1:

• Large messages serialized to direct buffers allocated a full-size heap array per write (Write direct buffers in place through their NIO view above 512 bytes streamnative/lightproto#20). 0.8.0 composed every message in a heap byte[] scratch before copying it into the target buffer; above 1 MiB the scratch was never retained, so every ~4.6 MB CommandGetTopicsOfNamespaceResponse cost a fresh multi-MB (G1 humongous) allocation — invisible to the broker's and proxy's AsyncDualMemoryLimiter, which accounts these responses as direct memory. 0.8.1 writes messages above 512 bytes in place through the direct buffer's NIO view: no scratch array, no copy, no allocation at any size.
• Reused message instances retained the previous message's data after clear() (Release data references in clear() for messages above CLEAR_RETAIN_MAX streamnative/lightproto#19). 0.8.0's O(1) clear() only reset counts and presence bits, so the per-connection BaseCommand in PulsarDecoder kept the last topic list (~4.6 MB) alive on every connection that had ever received one. 0.8.1 releases those references for messages above 64 KiB.

With 0.8.1 the test passes locally (500/500 requests, free-heap floor >50 MB, where 0.8.0 ran out of heap at 275/500).

The performance gains that motivated the upgrade are retained. Measured on Pulsar's protocol messages against 0.7.3 (JDK 26, interleaved A/B, time per operation):

	v0.7.3	v0.8.1	Δ
BaseCommand serialize	52.3 ns	23.0 ns	−56%
MessageMetadata serialize	81.2 ns	70.4 ns	−13%
BaseCommand deserialize	28.5 ns	21.9 ns	−23%
MessageMetadata deserialize	72.5 ns	43.0 ns	−41%
4.6 MB topic-list response serialize	175 µs	166 µs	−5% (0 B allocated)

Main changes in the generated code since 0.7.3: O(1) clear() with presence-guarded getters, presence-bit-driven traversal for union-like messages such as BaseCommand, array/NIO-view serialization with no sun.misc.Unsafe in the hot loops (JDK 24+ taxes each call), unchecked Netty reads for 64-bit varints.

Modifications

• Bump lightproto from 0.7.3 to 0.8.1 in gradle/libs.versions.toml; all modules applying the plugin pick it up via the version catalog.

Verifying this change

• Make sure that the change passes the CI checks.

ProxyPatternConsumerBackPressureMultipleConsumersTest (the test that OOMed on 0.8.0) passes locally on this branch with the released 0.8.1 artifacts.

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency): io.streamnative.lightproto 0.7.3 → 0.8.1 (code generator and Gradle plugin; the generated protocol classes change, the wire format does not)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment