Fix Metal renderer crash in packaged apps (Bundle.module fatalErrors) (#593)

MetalTerminalRenderer.candidateBundles() included Bundle.module as its
first candidate for locating SwiftTerm_SwiftTerm.bundle (the shaders).
SwiftPM's generated accessor for executable targets doesn't behave like
a normal Bundle lookup: it fatalErrors (aborting the whole process, not
throwing or returning nil) if the bundle isn't found at either of its
two hardcoded candidates - Bundle.main.bundleURL (the .app's root, not
Contents/Resources where a packaged .app actually places SwiftPM
resource bundles) or the build machine's absolute .build/.../
SwiftTerm_SwiftTerm.bundle path baked into the binary at compile time.

The practical effect: any app that depends on this package via SPM,
ships the resource bundle correctly in its own build pipeline, and
enables the Metal renderer will crash instantly on any machine other
than the one that built it - candidateBundles()'s other two fallbacks
(Bundle(for:), Bundle.main) never get a chance to run, because merely
evaluating the Bundle.module property is what crashes.

Fix: probe for the same bundle by name ourselves via Bundle(url:),
which is a normal failable initializer (verified it returns nil for a
missing path and a working bundle for a present one, no fatalError
either way) - mirroring the generated accessor's own main-bundle-
relative lookup, plus the Contents/Resources location it misses. Falls
through to the existing fallback candidates exactly as before for any
environment where the old code didn't crash.

Author: mcglothi

Sources/SwiftTerm/Apple/Metal/MetalTerminalRenderer.swift

@@ -2770,7 +2770,30 @@ final class MetalTerminalRenderer: NSObject, MTKViewDelegate {
     private static func candidateBundles() -> [Bundle] {
         var bundles: [Bundle] = []
         #if SWIFT_PACKAGE
-        bundles.append(Bundle.module)
+        // Deliberately not `Bundle.module`: SwiftPM's generated accessor for
+        // executable targets calls `fatalError` (aborting the whole process,
+        // not throwing) instead of returning nil when it can't locate
+        // `SwiftTerm_SwiftTerm.bundle`. Its only two candidates are
+        // `Bundle.main.bundleURL` (the .app's *root*, not `Contents/Resources`
+        // where a packaged .app actually puts SwiftPM resource bundles) and
+        // the build machine's absolute `.build/.../SwiftTerm_SwiftTerm.bundle`
+        // path baked into the binary at compile time. That means any app that
+        // bundles this package and ships the resource bundle correctly still
+        // crashes the instant Metal rendering is requested on a machine other
+        // than the one that built it. Probe for the same bundle name
+        // ourselves — mirroring the accessor's own main-bundle-relative
+        // lookup, plus the `Contents/Resources` location it misses — so a
+        // missing bundle falls through to the next candidate instead of
+        // aborting the process.
+        let bundleName = "SwiftTerm_SwiftTerm.bundle"
+        if let url = Bundle.main.resourceURL?.appendingPathComponent(bundleName),
+           let resourceBundle = Bundle(url: url) {
+            bundles.append(resourceBundle)
+        }
+        if let url = Bundle.main.bundleURL.appendingPathComponent(bundleName) as URL?,
+           let resourceBundle = Bundle(url: url) {
+            bundles.append(resourceBundle)
+        }
         #endif
         bundles.append(Bundle(for: MetalTerminalRenderer.self))
         bundles.append(Bundle.main)