docker: Update Fedora base image to 40

- Upgraded Fedora base image from 35 to 40. The existing Cargo failures were caused by the outdated Rust toolchain in Fedora 35. Cargo lockfile format v4 was introduced in Cargo 1.84 (December 2024), while Fedora 35 provides a Rust/Cargo version from roughly 2021–2022. As a result, the system Cargo could not parse modern Cargo.lock files, making it incompatible with current Rust projects.

- Added missing build dependencies to the Dockerfile, most notably the protobuf compiler (protoc).

Changelog-None: Upgraded Fedora version to 40 for reproducible build.

contrib/docker/Dockerfile.builder.fedora

@@ -1,4 +1,4 @@
-FROM fedora:35
+FROM fedora:40
 
 ENV UV_PYTHON=3.12
 ENV BITCOIN_VERSION=27.1
@@ -21,8 +21,25 @@ RUN dnf update -y && \
 		xz \
 		zlib-devel \
 		cargo \
-		libsodium-devel && \
-	wget https://github.com/kristapsdz/lowdown/archive/refs/tags/VERSION_1_0_2.tar.gz && \
+		libsodium-devel \
+		which \
+		sed \
+		gettext-devel \
+		gmp-devel \
+		python3-devel \
+		python3-pip \
+		python3-poetry \
+		postgresql-devel \
+		protobuf-compiler \
+		protobuf-devel && \
+	dnf clean all
+
+# Install Rust via rustup (for lockfile v4 support)
+RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --default-toolchain stable
+ENV PATH="/root/.cargo/bin:${PATH}"
+
+# Install lowdown
+RUN wget https://github.com/kristapsdz/lowdown/archive/refs/tags/VERSION_1_0_2.tar.gz && \
 	tar -xzf VERSION_1_0_2.tar.gz && \
 	cd lowdown-VERSION_1_0_2 && \
 	./configure && \
@@ -30,9 +47,9 @@ RUN dnf update -y && \
 	make install && \
 	ldconfig && \
 	cd /tmp && \
-	rm -rf VERSION_1_0_2.tar.gz lowdown-VERSION_1_0_2 && \
-	dnf clean all
+	rm -rf VERSION_1_0_2.tar.gz lowdown-VERSION_1_0_2
 
+# Install Bitcoin Core
 RUN wget https://storage.googleapis.com/c-lightning-tests/bitcoind/bitcoin-${BITCOIN_VERSION}-x86_64-linux-gnu.tar.gz \
     -O bitcoin.tar.gz && \
     tar -xvzf bitcoin.tar.gz && \
@@ -42,6 +59,6 @@ RUN wget https://storage.googleapis.com/c-lightning-tests/bitcoind/bitcoin-${BIT
     mv bitcoin-$BITCOIN_VERSION/share/man/man1/* /usr/share/man/man1 && \
     rm -rf bitcoin.tar.gz bitcoin-$BITCOIN_VERSION
 
-# Ensure `uv` can be found
-ENV PATH=${PATH}:/root/.local/bin
+# Install uv
+ENV PATH="${PATH}:/root/.local/bin"
 RUN wget -qO- https://astral.sh/uv/install.sh | sh