Possible regression / changed behavior in v10: `CasesCount` no longer maps from `Cases.Count` automatically

A pull request for this has already been merged.

• #916 by @DocSvartz — merged

Hi,

after upgrading Mapster from v7 to v10, I noticed a behavior change that used to work for us without explicit custom mapping.

## What changed

We have a destination/view model property like:

```csharp
public int CasesCount { get; set; }
```

and a source entity with a collection:

```csharp
public ICollection Cases { get; set; }
```

In Mapster v7, `CasesCount` was populated automatically (effectively from Cases.Count) even without any explicit .Map(...) configuration.

After upgrading to v10, the same property now gets value 0.

## Question

Was this behavior intentionally changed in v10?

- If yes, was it ever officially supported, or was it only incidental behavior?
- If no, could this be a regression?

## Minimal example

```csharp
public class Source
{
public ICollection Cases { get; set; } = new List
{
new Case(),
new Case(),
new Case()
};
}

public class Case
{
}

public class Destination
{
public int CasesCount { get; set; }
}
```

Expected: `CasesCount == 3`
Actual: `CasesCount == 0`

Start with the minimal Source, Case, and Destination example in the issue, then review merged pull request #916 for the relevant v10 behavior. Compare the result against the stated v7 expectation; done means the behavior is either confirmed and documented as intentional or covered by a regression fix and verification.

Written by the indexing model from the issue text.