BlobClient::GetProperties()/Download() throw std::out_of_range when a 2xx response omits x-ms-blob-type

**Describe the bug** `BlobClient::GetProperties()` and `BlobClient::Download()` throw `std::out_of_range` (from `std::map::at`) — not an `Azure::Storage::StorageException` / `Azure::Core::RequestFailedException` — when the service returns a successful (2xx) response that does not include the `x-ms-blob-type` response header. The Get Blob and Get Blob Properties readers deserialize the header unconditionally: ```cpp response.BlobType = Models::BlobType(pRawResponse->GetHeaders().at("x-ms-blob-type")); ``` `x-ms-blob-type` is generated as **required** (a bare `.at(...)`), whereas every *optional* header in the same reader — including `ETag` and `Last-Modified` — is read behind a `GetHeaders().count(...) != 0` guard. When a 2xx response omits the header, `std::map::at` throws `std::out_of_range`, which a caller's `catch (const StorageException&)` does not catch, and which aborts an otherwise-usable read (size, ETag, content range are all present; the read path frequently does not use `BlobType`). ***Exception or Stack Trace*** ``` terminate called after throwing an instance of 'std::out_of_range' what(): map::at ``` Thrown from the `BlobClient::GetProperties` / `BlobClient::Download` response deserialization in `sdk/storage/azure-storage-blobs/src/rest_client.cpp`. **To Reproduce** Call `BlobClient::GetProperties()` or `BlobClient::Download()` against any endpoint that returns HTTP 200 without the `x-ms-blob-type` header. A concrete case: a `BlobClient` targeting the OneLake / ADLS Gen2 `*.dfs.fabric.microsoft.com` (DFS) endpoint — it answers Blob `Get Blob Properties` / `Get Blob` with 200 but omits `x-ms-blob-type` (the blob-protocol response is served from the parallel `*.blob.fabric.microsoft.com` endpoint). ***Code Snippet*** ```cpp // blobClient targets a host that returns 200 without x-ms-blob-type auto blobClient = Azure::Storage::Blobs::BlobClient(url, credential); auto props = blobClient.GetProperties(); // throws std::out_of_range ``` **Expected behavior** The call should not throw `std::out_of_range`. A missing `x-ms-blob-type` on an otherwise-successful response should be tolerated — e.g. `BlobType` left as a default `Models::BlobType` — consistent with how `ETag` / `Last-Modified` are already handled on the same responses. (If a missing required header is to be treated as an error, it should at least surface as a typed exception, not a raw `std::out_of_range`.) **Setup (please complete the following information):** - OS: any (platform-independent response-parsing path) - Version of the Library used: `azure-storage-blobs`, reproduced on current `main` (also present in released 12.x) **Additional context** Mirrors the existing "striped blob" compatibility fix for `x-ms-blob-sequence-number` (PR #3932, commit 0e00a3a5), which marked a similarly-required header optional via an `x-nullable` swagger directive plus the matching generated-file guard. A PR taking the same approach for `x-ms-blob-type` on `Blob_GetProperties` and `Blob_Download` follows. **Information Checklist** - [x] Bug Description Added - [x] Repro Steps Added - [x] Setup information Added