Add property operator implementations with support for multiple values

[konard]

Summary

This pull request implements the requested feature from issue #125 by adding property operator implementations that support multiple values.

Fixes

Fixes #125

Implementation Details

New Property Operators

1. MultipleValuesPropertyOperator<TLinkAddress>

Extends the existing PropertyOperator to store and manage multiple values for a single property.

Key Features:

• GetAll(link) - Returns all values for a property
• GetFirst(link) - Returns the first value (maintains compatibility)
• Add(link, value) - Adds a value without replacing existing ones
• Remove(link, value) - Removes a specific value
• Set(link, values) - Replaces all values with a new set
• Clear(link) - Removes all values
• Contains(link, value) - Checks if a value exists
• Count(link) - Returns the number of values

2. MultipleValuesPropertiesOperator<TLinkAddress>

Extends the existing PropertiesOperator to handle multiple values for object-property combinations.

Key Features:

• GetAllValues(object, property) - Returns all values for an object-property pair
• AddValue(object, property, value) - Adds a value
• RemoveValue(object, property, value) - Removes a specific value
• SetAllValues(object, property, values) - Replaces all values
• ClearAllValues(object, property) - Removes all values
• ContainsValue(object, property, value) - Checks if a value exists
• CountValues(object, property) - Returns the number of values

Architecture

Both operators follow the existing codebase patterns:

• Extend LinksOperatorBase<TLinkAddress>
• Use the same generic constraints as existing operators
• Maintain compatibility with the current ILinks interface
• Follow the established coding style and documentation patterns

Test Coverage

Comprehensive test suites have been added for both operators covering:

• Adding multiple values
• Removing specific values
• Setting/replacing all values
• Clearing all values
• Counting values
• Checking value existence
• Edge cases (non-existent properties, duplicate values, etc.)
• Multi-object scenarios

Usage Example

// MultipleValuesPropertiesOperator usage
var propertiesOperator = new MultipleValuesPropertiesOperator<ulong>(links);

propertiesOperator.AddValue(person, nameProperty, "John");
propertiesOperator.AddValue(person, nameProperty, "Johnny"); 
propertiesOperator.AddValue(person, nameProperty, "Jon");

var names = propertiesOperator.GetAllValues(person, nameProperty).ToList();
// names contains: ["John", "Johnny", "Jon"]

propertiesOperator.RemoveValue(person, nameProperty, "Johnny");
// names now contains: ["John", "Jon"]

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