Call walproposer from Rust (#5403)

Create Rust bindings for C functions from walproposer. This allows to
write better tests with real walproposer code without spawning multiple
processes and starting up the whole environment.

`make walproposer-lib` stage was added to build static libraries
`libwalproposer.a`, `libpgport.a`, `libpgcommon.a`. These libraries can
be statically linked to any executable to call walproposer functions.

`libs/walproposer/src/walproposer.rs` contains
`test_simple_sync_safekeepers` to test that walproposer can be called
from Rust to emulate sync_safekeepers logic. It can also be used as a
usage example.

.github/workflows/build_and_test.yml

@@ -320,6 +320,9 @@ jobs:
       - name: Build neon extensions
         run: mold -run make neon-pg-ext -j$(nproc)
 
+      - name: Build walproposer-lib
+        run: mold -run make walproposer-lib -j$(nproc)
+
       - name: Run cargo build
         run: |
           ${cov_prefix} mold -run cargo build $CARGO_FLAGS $CARGO_FEATURES --bins --tests

.github/workflows/neon_extra_builds.yml

@@ -103,6 +103,9 @@ jobs:
       - name: Build neon extensions
         run: make neon-pg-ext -j$(nproc)
 
+      - name: Build walproposer-lib
+        run: make walproposer-lib -j$(nproc)
+
       - name: Run cargo build
         run: cargo build --all --release