🐛 Fix Docker builds: Update Rust 1.75→1.83 for edition2024 support

- Rust 1.75 (Nov 2023) too old for base64ct-1.8.0 dependency
- base64ct requires edition2024 features not in Cargo 1.75
- Local system uses Rust 1.89, need Docker parity
- Updated all 6 Dockerfile variants across 3 services

Fixes:
- ML training service Docker build
- Trading service Docker build
- Backtesting service Docker build

Related: Wave 125 Phase 3B Docker deployment

services/backtesting_service/Dockerfile.dev

@@ -7,7 +7,7 @@
 # =============================================================================
 # BUILDER STAGE - Development Build
 # =============================================================================
-FROM rust:1.75-slim as backtesting-dev-builder
+FROM rust:1.83-slim as backtesting-dev-builder
 
 # Install build dependencies
 RUN apt-get update && apt-get install -y \

services/backtesting_service/Dockerfile.production

@@ -7,7 +7,7 @@
 # =============================================================================
 # BUILDER STAGE - Optimized Build
 # =============================================================================
-FROM rust:1.75-slim as backtesting-builder
+FROM rust:1.83-slim as backtesting-builder
 
 # Install build dependencies
 RUN apt-get update && apt-get install -y \