feat: custom module install directory

[perazz]

Summary

This PR extends fpm to support installing compiled module files (.mod) to a custom directory separate from headers, providing better organization. Close #1157.

Changes

Manifest

• New optional module-dir field to [install] section
• Default: fallback to "include" directory (backward compatible)

Installer

• Extended installer_t with moduledir field and install_module() method (now separate from headers)

Example & Testing:

• Added example_packages/custom_module_dir/ demonstrating the feature
• Integrated internal and CI tests

Usage Example

[install]
library = true
module-dir = "custom/modules"  # Optional: defaults to "include"

[Copilot]

Pull Request Overview

This PR adds support for installing compiled Fortran module files (.mod) to a custom directory separate from headers, enhancing project organization and providing more flexible installation options.

• Added a new optional module-dir field to the [install] section of fpm.toml
• Extended the installer with a separate install_module() method and moduledir field
• Maintained backward compatibility by defaulting to the "include" directory when not specified

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/fpm/manifest/install.f90	Added module_dir field to install configuration with parsing and validation
src/fpm/installer.f90	Extended installer with moduledir field and separate install_module() method
src/fpm/cmd/install.f90	Updated to use new module installation method instead of header installation
test/fpm_test/test_manifest.f90	Added unit test for module directory configuration parsing
test/fpm_test/test_installer.f90	Added unit test for custom module directory installation
example_packages/custom_module_dir/*	Created example package demonstrating the new feature
ci/run_tests.sh	Added CI test to verify custom module directory functionality

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}