feat: add support for strictMemorySafety SwiftSetting and improve error handling

[pepicrft]

Summary

This PR adds support for the strictMemorySafety SwiftSetting introduced in Swift Package Manager 6.2 (SE-0458) and significantly improves error handling for malformed package settings.

Problem

When using Swift 6.2 with packages that enable strict memory safety checking via .strictMemorySafety(), Tuist was failing with cryptic decoding errors:

keyNotFound(CodingKeys(stringValue: "name", intValue: nil), Swift.DecodingError.Context(...))

This happened because:

1. XcodeGraph didn't support the new strictMemorySafety setting type
2. When the Kind decoder failed, it fell back to legacy format
3. The legacy format decoder threw unhelpful errors

Changes

1. Add strictMemorySafety Support

• Added strictMemorySafety case to SettingName enum
• Added strictMemorySafety(String) case to Kind enum
• Added decoder handler for strictMemorySafety in switch statement
• Added encoder handler for strictMemorySafety in switch statement

2. Improve Error Handling

Introduced SettingDecodingError that provides actionable diagnostics:

Before:

keyNotFound(CodingKeys(stringValue: "name", intValue: nil), ...)

After:

Failed to decode target build setting at 'targets.Index 3.settings.Index 0'.
Expected either 'kind' (Xcode 14+ format) or 'name' (legacy format) key, but neither was found.
Tool: swift
Available keys: tool, condition, kind

This usually indicates a malformed Package.swift manifest or an unsupported Swift Package Manager version.

Testing

• ✅ Build passes: swift build (3.53s)
• ✅ All existing tests pass
• ✅ Decoding now supports Swift 6.2 packages with strictMemorySafety

Context

• Swift 6.2 introduced strictMemorySafety setting per SE-0458
• This setting enables compiler checks for memory safety violations
• Packages using this setting were causing Tuist to fail during manifest parsing

🤖 Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com