tjson: Fix schema comparison

[rumyantseva]

This task is a part of #683 epic.

🎯 Currently, schema comparison method func (s *Schema) Equal(other *Schema) bool is implemented with reflect.DeepEqual. The goal of this task is to come up with a better approach.

The target code is located here.

Tigris' data types consist of type and format. For int64 and double format is not required but might be set.

Having that in mind, the following schemas must be equal:

	doubleSchema = &Schema{
		Type: Number,
	}
	doubleSchemaWithFormat = &Schema{
		Type:   Number,
		Format: Double,
	}

As well as:

	int64Schema = &Schema{
		Type: Integer,
	}
	int64SchemaWithFormat = &Schema{
		Type:   Integer,
		Format: Int64,
	}

We need to fix comparison to make such schemas equal.

Checklist:

• Have a look at the Tigris doc once again to make sure that int64 and double are the only cases that can cause different schemas need to be equal.
• Implement the changes and add tests to check that the comparison works equally for the different schemas that describe the same data type.

[rumyantseva]

@AlekSi I finalized the description for this task. Please have a look!