PipelineBuilder: consider FIFO instead of LIFO for intuitive middleware ordering

[JusterZhu]

Problem

PipelineBuilder uses ImmutableStack (LIFO) for middleware registration:

// Registration order (developer writes):
builder
    .UseMiddlewareIf<PatchMiddleware>(true)
    .UseMiddleware<CompressMiddleware>()
    .UseMiddleware<HashMiddleware>();

// Actual LIFO execution order: Hash -> Compress -> Patch

A developer naturally expects registration order to match execution order. The LIFO semantics caused a bug in MacStrategy (fixed in #436) where the registration order was wrong because the author expected FIFO behavior.

Proposal

Change ImmutableStack to ImmutableQueue (FIFO) or List<IMiddleware> with forward iteration. This would require reversing the registration order in WindowsStrategy and LinuxStrategy (which currently depend on LIFO to get Hash executed first).

Scope

• Pipeline/PipelineBuilder.cs
• Strategy/WindowsStrategy.cs
• Strategy/LinuxStrategy.cs
• Related PipelineBuilder tests

Priority

Low — the current code works correctly after #436, but this change would prevent future maintainers from making the same mistake.