Feat(Mapper): Support [Key] and [NotMapped] attributes from DataAnnotations

[lucafabbri]

This PR enhances the BsonMapper to recognize common attributes from System.ComponentModel.DataAnnotations, improving interoperability with other frameworks like Entity Framework.

Changes:

• [Key] as [BsonId]: The [Key] attribute is now recognized as an alias for [BsonId(AutoId = false)].

• [NotMapped] as [BsonIgnore]: The [NotMapped] attribute is now recognized as an alias for [BsonIgnore].

To avoid adding new dependencies to older target frameworks (like .NET Standard 2.0), this functionality is conditionally compiled and only active for projects targeting .NET 8 or newer (#if NET8_0_OR_GREATER).

Verification:

• Added new unit tests in CustomMapping_Tests.cs to verify that [Key] and [NotMapped] attributes are correctly handled.

• Added a new benchmark (InsertionIgnoreExpressionPropertyComponentModelBenchmark) to measure insertion performance when using property exclusion attributes.

[JKamsker]

Thanks for your contribution! Please see my comments.

[JKamsker]

@codex review

[chatgpt-codex-connector[bot]]

Codex Review: Didn't find any major issues. Keep them coming!

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