Merge HBApplication and HBApplicationBuilder

[adam-fowler]

It does mean the router has to be built before the application, as HBRouterBuilder would be a painful to setup as Sendable.
But the advantage of breaking out the router builder is it opens up other possibilities for other forms of route building.

let router = HBRouterBuilder()
router.middlewares.add(HBFileMiddleware())
router.get("test/") { _, context in
    return context.endpointPath
}
router.post("test2") { _, context in
    return context.endpointPath
}
let app = HBApplication(responder: router.buildResponder())
try await app.runService()

It does also mean the application isn't available when building routes, so data attached to application is not available (eg EventLoopGroup). But then we are trying to move away from HBApplication being a central source of data.

[codecov]

Codecov Report

Attention: 16 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
...Hummingbird/Server/Application+HTTPResponder.swift	100.00% <100.00%> (ø)
...rces/Hummingbird/Storage/MemoryPersistDriver.swift	70.90% <100.00%> (+0.53%)	⬆️
...s/HummingbirdFoundation/Files/FileMiddleware.swift	95.90% <ø> (ø)
Sources/HummingbirdXCT/Application+XCT.swift	100.00% <100.00%> (ø)
Sources/HummingbirdXCT/HBXCTLive.swift	93.15% <100.00%> (+0.09%)	⬆️
Sources/HummingbirdXCT/HBXCTRouter.swift	92.59% <100.00%> (-0.35%)	⬇️
Sources/Hummingbird/Application.swift	80.89% <76.81%> (-19.11%)	⬇️

... and 6 files with indirect coverage changes

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