Module records and aliases

Installation records what a module reports about itself. dpm_install_module
opens a module once, writes its version and description to a .meta file in
/var/lib/dpm/metadata/, and records the alternate names it declared in
modules.aliases beside it. dpm_uninstall_module removes both, leaving the
module file in place.

dpm_list_modules reads those records and opens no module. A module with no
record lists with a version of <uninstalled> and still loads when a caller
names it. An unreadable or absent metadata directory costs the listing its
detail and costs nothing else.

Aliases give a module alternate names, declared through the new
dpm_module_aliases contract symbol or added with dpm_add_module_alias. A
name is recorded once: one already serving as an alias, or belonging to an
installed module, is refused rather than repointed. dpm_require matches a
name against the installed modules, then the alias table, then the module
path.

The metadata directory is a fifth override field and the -M flag, and
[modules] metadata in core.conf.

The test suite is four binaries covering context, modules, records, and
aliases, each a ctest case of its own, alongside the CLI cases.

include/internal/sanitizers.hpp

@@ -32,4 +32,12 @@ namespace dpm_core {
      * @return The path, ending in a slash unless it is empty
      */
     std::string with_trailing_slash(std::string s);
+
+    /**
+     * @brief Strips leading and trailing whitespace
+     *
+     * @param s The string to trim
+     * @return The trimmed string; empty when the input is entirely whitespace
+     */
+    std::string trim(const std::string& s);
 } // namespace dpm_core