feat: update Makevars to support vendoring

.Rbuildignore

@@ -14,3 +14,4 @@
 ^Taskfile\.yml$
 ^\.task$
 ^src/\.cargo$
+^src/rust/vendor$

src/Makevars

@@ -8,8 +8,16 @@ all: C_clean
 $(SHLIB): $(STATLIB)
 
 CARGOTMP = $(CURDIR)/.cargo
+VENDOR_DIR = ./rust/vendor
 
 $(STATLIB):
+	if [ -f ./rust/vendor.tar.xz ]; then \
+		mkdir -p $(VENDOR_DIR) && \
+		$(TAR) --extract --xz --file ./rust/vendor.tar.xz -C $(VENDOR_DIR) && \
+		mkdir -p ./rust/.cargo && \
+		cp ./rust/vendor-config.toml ./rust/.cargo/config.toml; \
+	fi
+
 	# In some environments, ~/.cargo/bin might not be included in PATH, so we need
 	# to set it here to ensure cargo can be invoked. It is appended to PATH and
 	# therefore is only used if cargo is absent from the user's PATH.
@@ -28,4 +36,4 @@ C_clean:
 	rm -Rf $(SHLIB) $(STATLIB) $(OBJECTS)
 
 clean:
-	rm -Rf $(SHLIB) $(STATLIB) $(OBJECTS) rust/target
+	rm -Rf $(SHLIB) $(STATLIB) $(OBJECTS) $(VENDOR_DIR) ./rust/target

src/Makevars.win

@@ -10,8 +10,16 @@ all: C_clean
 $(SHLIB): $(STATLIB)
 
 CARGOTMP = $(CURDIR)/.cargo
+VENDOR_DIR = ./rust/vendor
 
 $(STATLIB):
+	if [ -f ./rust/vendor.tar.xz ]; then \
+		mkdir -p $(VENDOR_DIR) && \
+		$(TAR) --extract --xz --file ./rust/vendor.tar.xz -C $(VENDOR_DIR) && \
+		mkdir -p ./rust/.cargo && \
+		cp ./rust/vendor-config.toml ./rust/.cargo/config.toml; \
+	fi
+
 	mkdir -p $(TARGET_DIR)/libgcc_mock
 	# `rustc` adds `-lgcc_eh` flags to the compiler, but Rtools' GCC doesn't have
 	# `libgcc_eh` due to the compilation settings. So, in order to please the
@@ -38,4 +46,4 @@ C_clean:
 	rm -Rf $(SHLIB) $(STATLIB) $(OBJECTS)
 
 clean:
-	rm -Rf $(SHLIB) $(STATLIB) $(OBJECTS) rust/target
+	rm -Rf $(SHLIB) $(STATLIB) $(OBJECTS) $(VENDOR_DIR) ./rust/target