- Updated `EnvelopeGenerator.Extensions.csproj` to include
`Microsoft.Extensions.Caching.Memory` package.
- Refactored `HistoryController` to use `IMemoryCache` for
caching functionality.
- Replaced manual dictionary creation in `GetReferenceTypes`
with a call to `GetEnumAsDictionary<ReferenceType>()`.
- Changed enum type in `GetEnvelopeStatus` to
`ReferenceType` for consistency.
- Introduced `MemoryCacheExtensions` class with
`GetEnumAsDictionary<TEnum>` method for efficient enum
to dictionary conversion.
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