Add idempotent behavior to loader handle loading

[SATVIKsynopsis]

Description

Implemented idempotent load behavior in loader_impl.c for load_from_file, load_from_memory, load_from_package, and loader_impl_handle_initialize. When a handle is already loaded, returns success instead of erroring, and assign the existing handle to *handle_ptr if provided.

Fixes #644

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Documentation update

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