perf: add sccache to Docker builds for faster compilation

- Install sccache in builder stage of both api and indexer Dockerfiles
- Configure RUSTC_WRAPPER to use sccache
- Use Docker cache mount (--mount=type=cache,target=/sccache) to persist cache
- Reduces build time significantly on subsequent builds by caching compiled artifacts
- Requires Docker BuildKit (enabled by default in Docker 23.0+)

Note: First build will still be slow (installs sccache + populates cache)
Subsequent builds will be much faster as dependencies are cached

apps/indexer/Dockerfile

@@ -1,6 +1,11 @@
 FROM rust:1-bookworm AS builder
 WORKDIR /app
 
+# Install sccache for faster builds
+RUN cargo install sccache --locked
+ENV RUSTC_WRAPPER=sccache
+ENV SCCACHE_DIR=/sccache
+
 COPY Cargo.toml ./
 COPY apps/api/Cargo.toml apps/api/Cargo.toml
 COPY apps/indexer/Cargo.toml apps/indexer/Cargo.toml
@@ -11,7 +16,9 @@ COPY apps/indexer/src apps/indexer/src
 COPY crates/core/src crates/core/src
 COPY crates/parsers/src crates/parsers/src
 
-RUN cargo build --release -p indexer
+# Build with sccache (cache persisted between builds via Docker cache mount)
+RUN --mount=type=cache,target=/sccache \
+    cargo build --release -p indexer
 
 FROM debian:bookworm-slim
 RUN apt-get update && apt-get install -y --no-install-recommends ca-certificates wget unrar-free && rm -rf /var/lib/apt/lists/*