feat: add cross-compilation support with --target flag

- Updated build and run commands to accept a --target option for specifying target platforms.
- Enhanced documentation to include cross-compilation usage and supported targets.
- Modified configuration to allow target-specific settings and toolchains.
- Introduced a new test command to run project tests with specified profiles and targets.
- Improved handling of target directories and output structure for different platforms.
- Added support for multiple targets in the configuration file.
- Implemented inheritance for workspace and dependencies based on target and profile.

docs/dependencies-and-build/compilers-and-linking.md

@@ -17,7 +17,7 @@ DCR picks a backend from `build.compiler`:
 - Source files are found recursively in `src/` based on `build.language`.
 - `build.roots` and `build.src_disable` can replace the default `src/` root.
 - Mixed language builds use arrays, for example `build.language = ["c", "asm"]`.
-- Each source is compiled to `target/<profile>/obj/<relative-path>.o` (`.obj` on MSVC).
+- Each source is compiled to `target/<target>/<profile>/obj/<relative-path>.o` (`.obj` on MSVC, where `<target>` is `native` or target triple).
 - Recompile happens when source mtime is newer than object mtime.
 - `build.exclude` removes paths from source/header collection; `build.include` re-allows matching paths and has priority over `exclude`.
 
@@ -35,6 +35,8 @@ MSVC:
 - `debug`: `/Od /Zi /W4 /DDCR_DEBUG /Oy-`
 - `release`: `/O2 /DNDEBUG`
 
+Note: If custom `cflags` are set in `dcr.toml`, default profile flags are disabled to allow full control.
+
 ## Platform hint
 
 If `build.platform` is set, DCR passes it as an architecture hint: