Temp fix iOS build for Xcode 26.4

[nw-sentry]

Summary

Latest Xcode 26.4's newer clang rejects the fmt pod's FMT_COMPILE_STRING path with
"call to consteval function 'fmt::basic_format_string<...>' is not a constant expression"

This breaks pod install → xcodebuild

This PR works around that by building the fmt pod against C++17 where the consteval constant-evaluation is more lenient, unblocking local iOS builds without touching React Native or Sentry SDK versions.

Changes

• ios/Podfile: Added a post_install block that sets CLANG_CXX_LANGUAGE_STANDARD = c++17 on the fmt pod's build configurations.
• ios/Podfile.lock: Updated PODFILE CHECKSUM (automatic)
• ios/sentry_react_native.xcodeproj/project.pbxproj: CocoaPods integration churn written by pod install under CocoaPods 1.16.2 — drops redundant empty inputPaths/outputPaths entries on the [CP] Embed Pods Frameworks and [CP] Copy Pods Resources script phases, and clears a stale CC override that pointed at the ccache-clang wrapper. No behavioral change beyond making the committed project match what CocoaPods generates on current toolchains.

Test plan

• cd ios && pod install completes cleanly on Xcode 26.4
• npm run build-dev-ios builds and launches on the iOS simulator
• Android build (npm run build-dev-android) unaffected

[antonis]

LGTM 🚀