fix(ios): patch fmt consteval build error on Xcode 26.4+ (#28225)

## **Description**

Xcode 26.4 (Apple Clang 21) introduces stricter `consteval` enforcement
that breaks the `fmt` library (v11.0.2) bundled via `RCT-Folly`, causing
5 compilation errors in `format-inl.h`.

This patches `fmt/base.h` in the Podfile `post_install` block to disable
`consteval` for all Apple Clang versions, falling back to `constexpr`.
Same approach as the existing Folly coroutines patch. Safe for older
Xcode versions — `constexpr` is the default fallback `fmt` already uses
on many platforms. Survives `yarn setup` / `pod install` since the patch
is re-applied each time.

## **Changelog**

CHANGELOG entry: null

## **Related issues**

Fixes: N/A — build breakage on Xcode 26.4+

## **Manual testing steps**

```gherkin
Feature: iOS build with Xcode 26.4

  Scenario: developer builds iOS app
    Given Xcode 26.4 with Apple Clang 21 is installed

    When developer runs yarn start:ios
    Then the build completes without fmt consteval errors
```

## **Screenshots/Recordings**

<!-- Not applicable — build fix only -->

### **Before**

Build fails with 5 `consteval` errors in
`ios/Pods/fmt/include/fmt/format-inl.h`

### **After**

Build succeeds

## **Pre-merge author checklist**

- [x] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Mobile
Coding
Standards](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [ ] I've included tests if applicable
- [ ] I've documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [ ] I've applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Medium Risk**
> Adds a CocoaPods `post_install` patch that rewrites a vendored `fmt`
header, which could affect formatting code generation or conflict with
future `fmt` updates, but is limited in scope to a single preprocessor
toggle during install.
> 
> **Overview**
> Prevents Xcode 26.4+ build failures by extending the `Podfile`
`post_install` step to patch `fmt/include/fmt/base.h`, forcing
`FMT_USE_CONSTEVAL` from `1` to `0` (with a regex tolerant of
whitespace/indentation) and handling file permissions similarly to the
existing Folly patch.
> 
> Updates `Podfile.lock` with the new `PODFILE CHECKSUM` reflecting the
`Podfile` change.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
2c4aba0. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: abretonc7s

ios/Podfile

@@ -163,6 +163,24 @@ post_install do |installer|
     end
   end
 
+  # Fix fmt compilation error with Xcode 26 / Clang 21 consteval strictness
+  # Directly disable FMT_USE_CONSTEVAL rather than patching the detection logic.
+  # Uses regex to handle indented preprocessor directives (e.g. "#  define").
+  Dir.glob(installer.sandbox.root + "fmt/include/fmt/base.h") do |file|
+    begin
+      system "chmod +w #{file}"
+      contents = File.read(file)
+      modified = contents.gsub(/#\s*define FMT_USE_CONSTEVAL 1/, '#define FMT_USE_CONSTEVAL 0')
+      if !File.writable?(file)
+        system "sudo chmod +w #{file}"
+      end
+      File.write(file, modified)
+      system "chmod -w #{file}"
+    rescue => e
+      Pod::UI.warn "Failed to modify fmt base.h: #{e.message}"
+    end
+  end
+
   # This is necessary for Xcode 14, because it signs resource bundles by default
   # when building for devices.
   installer.target_installation_results.pod_target_installation_results

ios/Podfile.lock

@@ -4875,6 +4875,6 @@ SPEC CHECKSUMS:
   Yoga: 728df40394d49f3f471688747cf558158b3a3bd1
   YttriumWrapper: cbddb60c835ebc4232d9f57064084ab30686a18e
 
-PODFILE CHECKSUM: 03e4337c8a46ec38235554e231071c616488b29a
+PODFILE CHECKSUM: 41ec3b10789f39c64e75ca60eb74e86257e8f76d
 
 COCOAPODS: 1.16.2