refactor: migrate MICRO_PIP to fine-grained feature flags

Replace monolithic MICRO_PIP/PIP_MICRO with granular flags:

Feature flags (CMake options + platform auto-detection):
- PIP_NO_FILESYSTEM, PIP_NO_THREADS, PIP_NO_SOCKET
- PIP_NO_PROCESS, PIP_NO_DYNLIB, PIP_NO_FFT, PIP_NO_SERIAL

Embedded optimization flag:
- PIP_EMBEDDED (auto-set for Pico SDK and FreeRTOS)
  Controls buffer sizes, time stubs, terminal fallback, init stubs

Platform blocks in CMakeLists.txt:
- Pico SDK: auto-disables FS, PROCESS, DYNLIB, FFT, SERIAL;
  conditionally disables THREADS (no FreeRTOS) and SOCKET (no LWIP)
- FreeRTOS: auto-disables FS, PROCESS, DYNLIB, FFT, SERIAL;
  conditionally disables SOCKET (no LWIP)
- Android: auto-disables PROCESS, DYNLIB, FFT

Updated 96 files across libs/, utils/, tests/, and CMakeLists.txt.
Builds verified for Linux (547 tests pass) and Pico SDK (100%).
Removed all MICRO_PIP and PIP_MICRO references (0 remaining).

AGENTS.md

@@ -5,7 +5,7 @@
 ### Basic Build
 ```bash
 # Configure with CMake (release build)
-cmake -B build -j16
+cmake -B build
 
 # Build the project
 cmake --build build -j16
@@ -14,12 +14,12 @@ cmake --build build -j16
 cmake --build build --target install -j16
 
 # Local install (bin/lib/include in build directory)
-cmake -B build -DLOCAL=ON -j16
+cmake -B build -DLOCAL=ON
 ```
 
 ### With Tests
 ```bash
-cmake -B build -DTESTS=ON -j16
+cmake -B build -DTESTS=ON -DTESTS_RUN=ON
 cmake --build build -j16
 cd build && ctest
 ```