Adopt Xcode recommended settings and fix resulting build errors

Applied Xcode's "Update to recommended settings" (new warning flags,
LastUpgradeCheck 2650, scheme bumps, Info.plist tidy-up), then fixed the
build failures those stricter checks surfaced:

- Disable ENABLE_MODULE_VERIFIER and CLANG_WARN_QUOTED_INCLUDE_IN_FRAMEWORK_HEADER:
  the library intentionally uses quoted includes so the flat include/
  symlink directory resolves them for SPM; the module verifier rejects
  that.
- Add (void) to the GCDWebServerInitializeFunctions and
  _ExecuteMainThreadRunLoopSources definitions (CLANG_WARN_STRICT_PROTOTYPES
  + -Werror).
- Cast both branches of the status-code ternary in
  GCDWebServerConnection to NSInteger (-Wenum-compare-conditional mixed
  two enum types).

Verified: Run-Tests.sh, swift build, and the Xcode framework build all pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

GCDWebServer.xcodeproj/xcshareddata/xcschemes/GCDWebServers (Mac).xcscheme

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <Scheme
-   LastUpgradeVersion = "1130"
+   LastUpgradeVersion = "2650"
    version = "1.3">
    <BuildAction
       parallelizeBuildables = "YES"

GCDWebServer.xcodeproj/xcshareddata/xcschemes/GCDWebServers (iOS).xcscheme

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <Scheme
-   LastUpgradeVersion = "1130"
+   LastUpgradeVersion = "2650"
    version = "1.3">
    <BuildAction
       parallelizeBuildables = "YES"

GCDWebServer.xcodeproj/xcshareddata/xcschemes/GCDWebServers (tvOS).xcscheme

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <Scheme
-   LastUpgradeVersion = "1130"
+   LastUpgradeVersion = "2650"
    version = "1.3">
    <BuildAction
       parallelizeBuildables = "YES"