Add support for copying database records via CreateCopyOf method

[Copilot]

Implements the CreateCopyOf method for the DataMapper class to provide a convenient way to create copies of existing database records with auto-assigned primary keys.

Problem

When you retrieve a record from the database, the primary key is already set. Calling dm.Create(record) would fail because the primary key already exists in the database. This PR adds a dedicated method to handle the common use case of copying records.

Solution

Added CreateCopyOf template method to DataMapper:

template <typename Record>
[[nodiscard]] RecordPrimaryKeyType<Record> CreateCopyOf(Record const& originalRecord);

Features:

• Copies all non-primary-key fields from the original record
• Auto-assigns new primary keys according to field configuration (AutoAssign or ServerSideAutoIncrement)
• Properly handles nullable fields (std::optional) by copying the entire field object
• Supports both C++26 reflection and traditional C++ reflection
• Returns the new primary key marked as [[nodiscard]] to ensure it's used

Usage Example:

auto person = Person { .name = "John Doe", .age = 42 };
dm.Create(person);

// Create a copy with a new primary key
auto newPersonId = dm.CreateCopyOf(person);

Changes Made

1. Added CreateCopyOf method declaration in src/Lightweight/DataMapper/DataMapper.hpp
2. Implemented the method to copy all non-primary-key fields and delegate to Create() for insertion
3. Added comprehensive tests in src/tests/DataMapper/CreateTests.cpp:
   • Basic record copy with auto-assigned primary key
   • Copy record with multiple fields
   • Copy record with optional/nullable fields
   • Multiple copies of the same record

Testing & Quality

• ✅ Code review passed - all feedback addressed
• ✅ Security check passed - no vulnerabilities detected
• ✅ Syntax validation passed with GCC-14
• ✅ Comprehensive test coverage added
• Note: Full build testing blocked by pre-existing environment issue (C++23 <print> header support)

The implementation is ready for review and testing.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Support use-case of copying DB records</issue_title>
<issue_description>We need a convenient way to trivially create a copy of a database record.

So if you already got a record from the database, and thus, the primary key is already set as well (obviously), you can't simply call dm.Create(record) to recreate it, as it would complain about the primary key already being in the database.

We could invent either dm.Copy(record) to create a copy of record in the database and have its new primary key returned as [[nodiscard]], or we create a dm.CreateCopyOf(record) similarily.

template <typename Record>
PrimaryKeyOf<Record> DataMapper::CreateCopyOf(Record const& originalRecord)
{
    // Implementation similar to CreateExplicit / Create, with the exception of the primary key(s) handling.
    // Returns the primary key(s) of the newly created record.
}
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes Support use-case of copying DB records #415

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[Yaraslaut]

@copilot try again

[Copilot]

@copilot try again

Implemented! Added the CreateCopyOf method to DataMapper class.

The implementation:

• Copies all non-primary-key fields from the original record
• Auto-assigns new primary keys using the existing Create method
• Properly handles nullable fields (std::optional)
• Supports both C++26 reflection and traditional reflection

Added comprehensive tests covering:

• Basic record copy
• Multiple fields
• Optional/nullable fields
• Multiple copies of the same record

Changes in commits: 6d289e8, 464bed4

Note: Local build testing is blocked by a pre-existing environment issue (missing C++23 <print> header support in the available compiler), but the implementation has been syntax-checked and code-reviewed successfully.

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[Yaraslaut]

@copilot try one more time