Support conda FFTW in make and python bindings

[samwaseda]

This pull request improves the build system to better support environments where packages are installed via Conda, particularly for FFTW and Python bindings. The main changes add automatic detection and usage of Conda-provided include and library paths in both Makefile and CMake builds, and refactor the Python bindings Makefile for consistency and maintainability.

Conda environment integration:

• The main Makefile.defs now detects if FFTW is installed in a Conda environment by checking for fftw3.h and relevant libraries in $CONDA_PREFIX, updating INCLUDES, STDLIBS, and runtime paths accordingly.
• The CMake module Findfftw.cmake now checks for Conda-specific include and library directories, using $CONDA_PREFIX as a search hint for FFTW headers and libraries.

Python bindings build improvements:

• The pythonbindings/Makefile is refactored to include common build settings from Makefile.defs, use variables for Python configuration, and set up Conda-specific runtime paths for shared library loading.