fix: upgrade Dockerfile to rust 1.88 for time 0.3.47 compatibility

time 0.3.47 (security fix for stack exhaustion DoS) requires rustc
1.88.0. Update Docker builder stage from rust:1.85-slim to
rust:1.88-slim.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ishaileshpant

Dockerfile

@@ -1,5 +1,5 @@
 # Stage 1: Build
-FROM rust:1.85-slim AS builder
+FROM rust:1.88-slim AS builder
 
 RUN apt-get update && apt-get install -y \
     protobuf-compiler \