Upgrade Azure generator TypeSpec dependencies to 1.9.0

[Copilot]

Description

Upgrades Azure generator TypeSpec dependencies to match upstream http-client-csharp@1.0.0-alpha.20260214.2. Fixes package-lock.json version mismatch and updates test projects for TypeSpec 1.9.0 compatibility.

TypeSpec core packages: 1.8.0 → 1.9.0

• @typespec/compiler, @typespec/http, @typespec/openapi, @typespec/json-schema

TypeSpec library packages: 0.78.0 → 0.79.0

• @typespec/rest, @typespec/versioning, @typespec/xml, @typespec/library-linter

Azure TypeSpec packages:

• @azure-tools/typespec-azure-core: 0.64.0 → 0.65.0
• @azure-tools/typespec-client-generator-core: 0.64.4 → 0.65.1

New dependencies:

• @typespec/sse@0.79.0, @typespec/streams@0.79.0

Test compatibility fix:
TypeSpec 1.9.0 validates for duplicate client names when generic unions are instantiated multiple times. Fixed BasicTypeSpec test by replacing generic Dfe<T> with concrete named unions:

// Before: Generic union causing duplicate name errors
union Dfe<T> { T, DataFactoryElementModel }
stringProperty: Dfe<string>;
intProperty: Dfe<int32>;

// After: Concrete unions with unique names
@clientName("DfeString", "csharp")
union DfeString { string, DataFactoryElementModel }

@clientName("DfeInt32", "csharp")
union DfeInt32 { int32, DataFactoryElementModel }

Related: TypeSpec commit 071cc29

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