Modules determine their own compatibility with the library

A module is built against the system-installed libdpm-core.so and is
responsible for being correct against it. Where it needs to act on the
version it is running under, dpm_core_version() reports that and the
module decides for itself.

dpm_module_core_min() is removed. It was a declaration handed to the
library to enforce on the module's behalf, and enforcement of that kind
belongs nowhere in a library that routes and hosts. The contract is now
three reserved symbols and load validation is two steps: the reserved
symbols resolve, and the version and description probes return
well-formed values.

compare_versions had no remaining caller and is removed; parse_version
stays for the well-formedness probe. The core_too_new fixture went with
the handshake it existed to exercise.

include/internal/modules.hpp

@@ -34,7 +34,6 @@ struct dpm_module {
     void*       handle = nullptr;
     std::string version;
     std::string description;
-    std::string core_min;
     int (*execute)(dpm_ctx*, const char*, int, char**) = nullptr;
 };
 

include/internal/version.hpp

@@ -1,6 +1,6 @@
 /**
  * @file version.hpp
- * @brief X.Y.Z version parsing and comparison
+ * @brief X.Y.Z version parsing
  *
  * @copyright Copyright (c) 2026 SILO GROUP LLC
  * @author Chris Punches <chris.punches@silogroup.org>
@@ -33,13 +33,4 @@ namespace dpmcore {
  */
 bool parse_version(const char* s, long out[3]);
 
-/**
- * @brief Compares two valid X.Y.Z version strings
- *
- * @param a First version
- * @param b Second version
- * @return -1 if a < b, 0 if equal, 1 if a > b
- */
-int compare_versions(const char* a, const char* b);
-
 } // namespace dpmcore