ReadAsync regression

[leecannon]

Prior versions of this library supported ReadAsync called with these generic parameters:

ReadAsync<string, TimeSpan?, TimeSpan?, string, bool>(sql)

But with newer versions this throws:

Norm.NormMultipleMappingsException: Multiple mappings requires types of same category:
    Classes with classes, records with records, value tuples with value tuple and simple types with simple types.
    For example pappings `Read<Class, int>` or `Read<int, Class>` are not permitted.

[vbilopav]

That exception meant to prevent mapping like this ReadAsync<string, Class>(sql) which is not supported.

However, it seems that .NET handles TimeSpan types a bit differently (there is no TypeCode unlike DateTime), so I had to fix that.

Package version 3.1.1. with this fix is being built and deployed at this moment.

I added a unit test for this issue:

Norm.net/Tests/PostgreSqlUnitTests/ReadTuplesUnitTests.cs

Line 394 in be6c564

public async Task ReadAsync_Regression_Issue1()

Also, support for instance mapping for TimeSpan has been added with the test also:

Norm.net/Tests/PostgreSqlUnitTests/QueryUnitTests.cs

Line 303 in be6c564

public async Task ReadAsync_Regression_Issue1()