fix(c examples): point loader at the build dir so pact_ffi's dylib is found

Since the C examples now link pact_ffi's cdylib (needed to pull in vendored
Lua), the loader must be able to find libpact_ffi.so/.dylib/.dll at runtime.
pact_ffi's build.rs intentionally gives the macOS dylib a bare install name
(for discovery via a well-known system path like /usr/local/lib), so it
isn't found relative to the executable; on Windows, corrosion copies the DLL
to the top-level build dir while multi-config generators place the .exe in
build/Release. Point LD_LIBRARY_PATH/DYLD_LIBRARY_PATH/PATH at ./build when
running the examples so the loader finds it on all three platforms.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: rholshausen

c/consumer/justfile

@@ -16,8 +16,8 @@ clean:
 
 [unix]
 run: build
-    ./build/pact-consumer
+    LD_LIBRARY_PATH="./build:${LD_LIBRARY_PATH:-}" DYLD_LIBRARY_PATH="./build:${DYLD_LIBRARY_PATH:-}" ./build/pact-consumer
 
 [windows]
 run: build
-    ./build/Release/pact-consumer.exe
+    PATH="./build:${PATH:-}" ./build/Release/pact-consumer.exe

c/provider/justfile

@@ -16,8 +16,8 @@ clean:
 
 [unix]
 run: build
-    ./build/pact-provider
+    LD_LIBRARY_PATH="./build:${LD_LIBRARY_PATH:-}" DYLD_LIBRARY_PATH="./build:${DYLD_LIBRARY_PATH:-}" ./build/pact-provider
 
 [windows]
 run: build
-    ./build/Release/pact-provider.exe
+    PATH="./build:${PATH:-}" ./build/Release/pact-provider.exe