Generic math structure

# Core interfaces

- [x] Approved
- [x] [Implemented](https://github.com/asc-community/AngouriMath/pull/509)

## IClosedArithmetics

```cs
public interface IClosedArithmetics
```

It will inherit `+`, `-`, `*`, also unary `+` and `-`.

## IHasNeutralValues

```cs
public interface IHasNeutralValues
: IAdditiveIdentity,
IMultiplicativeIdentity
```

## IScalarClosedArithmetics

```cs
public interface IScalarClosedArithmetics
: IClosedArithmetics,
IComparisonOperators
```

## IHasAbsoluteValue

```cs
public interface IHasAbsoluteValue
{
abstract static TOut Abs(TSelf self);
}
```

# Implementation relations

## Entity

It will implement `IClosedArithmetics`, `IDivisionOperators`, `IParseable`, `IHasAbsoluteValue`, and `IHasNeutralValues`.

## Complex

It will implement `IClosedArithmetics`, `IDivisionOperators`, `IHasAbsoluteValue`, `IHasNeutralValues`.

## Real

It will implement `IScalarClosedArithmetics`, `IDivisionOperators`, `IHasAbsoluteValue`, `IHasNeutralValues`.

## Rational

It will implement `IScalarClosedArithmetics`, `IDivisionOperators`, `IHasAbsoluteValue`, `IHasNeutralValues`.

## Integer

It will implement `IScalarClosedArithmetics`, `IDivisionOperators`, `IHasAbsoluteValue`, `IHasNeutralValues`.

## Matrix

It will implement `IClosedArithmetics`.

# Applied to

.NET 6+ thanks to the `NET6_0` variable.

Review pull request 509 and the existing Entity, Complex, Real, Rational, Integer, and Matrix types. Check the NET6_0-gated generic-math interfaces and implementation relations listed here; the work is done when those declarations and relations match the approved specification.

Written by the indexing model from the issue text.