test: add calculator FastRPC example

test/src/calculator/README.md

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+# Calculator FastRPC Example
+
+Minimal FastRPC example offloading `sum` and `max` to the Hexagon DSP.
+Supports unsigned PDs only.
+
+## Layout
+
+```
+calculator/
+├── inc/                        calculator.h (QAIC-generated), calculator_test.h
+├── apps/                       Linux host side
+│   └── src/
+│       ├── calculator_stub.c   QAIC-generated stub
+│       └── calculator_test.c   Test logic
+├── hexagon/                    Hexagon DSP side
+│   └── src/
+│       ├── calculator_skel.c   QAIC-generated skeleton
+│       └── calculator_imp.c    DSP implementation
+└── calculator.idl              Interface definition
+```
+
+## Prerequisites
+
+- `clang` and `ld.lld`
+- `libcdsprpc.so.1.0.0` — built from the fastrpc project (required at link time for the host library)
+- `QAIC` — to regenerate `calculator.h`, `calculator_stub.c`, and `calculator_skel.c` from `calculator.idl`
+  - Source: https://github.com/qualcomm/QAIC.git
+  - `AEEStdDef.idl` and `remote.idl` from the Hexagon SDK are required dependencies, place them
+    in an `idl/` directory alongside `calculator.idl`, then run:
+    ```bash
+    ./qaic -I./idl calculator.idl -st
+    ```
+
+## Build
+
+> **Note:** `Makefile.am` for autotools integration will be added once the QAIC compiler
+> is available and the IDL dependencies (`AEEStdDef.idl`, `remote.idl`) are in place.
+
+
+Set `ROOT` to the fastrpc repo root before building.
+
+**DSP skeleton:**
+```bash
+cd hexagon/
+mkdir -p obj
+for f in src/*.c; do
+    clang --target=hexagon -fPIC -Wall -Werror \
+        -I"../inc" -I"$ROOT/inc" \
+        -c "$f" -o "obj/$(basename ${f%.c}.o)"
+done
+ld.lld -shared -soname=libcalculator_skel.so \
+    -z separate-loadable-segments \
+    -o libcalculator_skel.so obj/*.o
+```
+
+**Host library:**
+```bash
+cd apps/
+mkdir -p obj
+for f in src/*.c; do
+    clang --target=aarch64-linux-gnu -fPIC -Wall -Werror \
+        -I"../inc" -I"$ROOT/inc" \
+        -c "$f" -o "obj/$(basename ${f%.c}.o)"
+done
+ld.lld -shared -soname=libcalculator.so \
+    -o libcalculator.so obj/*.o \
+    "$ROOT/src/.libs/libcdsprpc.so.1.0.0"
+```
+
+## Deploy & Run
+
+Copy the libraries to the target device:
+
+```bash
+# Host stub
+cp apps/libcalculator.so /usr/lib/fastrpc_test/
+
+# DSP skeleton
+cp hexagon/libcalculator_skel.so /usr/share/fastrpc_test/v68/
+```
+
+Run using the `fastrpc_test` binary (CDSP, unsigned PD only):
+
+```bash
+fastrpc_test -d 3 -U 1
+```