fix: make DynaLoader::bootstrap delegate to XSLoader::load fallback chain

[fglock]

Summary

DynaLoader::bootstrap() previously always died with "Can't load module", making all DynaLoader-based XS modules fail immediately at load time. This prevented modules like Image::Magick, Tk, and others that use DynaLoader instead of XSLoader from loading at all.

Meanwhile, XSLoader::load() already had a sophisticated multi-stage fallback:

1. Java XS class found → initialize and return true
2. @ISA has functional parent → return true (inheritance fallback)
3. ::PP companion loaded → return true
4. die with "Can't load loadable object..." (matches /loadable object/ pattern for CPAN fallback detection)

Changes

• DynaLoader.java: delegate bootstrap() to XSLoader.load() instead of unconditionally dying
• DynaLoader.pm: Perl-side fallback also delegates to XSLoader::load
• ImageMagick.java: stub Java class with no-op UNLOAD() and constant() so Image::Magick loads cleanly

Before / After

	Before	After
use Image::Magick	Dies: "Can't load module Image::Magick"	Succeeds
Image::Magick->new	N/A (can't load)	Creates object
eval { require Image::Magick }	Sets $@, module unusable	Succeeds, $@ empty
Error message pattern	"Can't load module" (non-standard)	"Can't load loadable object..." (matches CPAN fallback pattern)

Impact

This fix improves CPAN compatibility broadly — any module using DynaLoader instead of XSLoader now gets the same fallback behavior. The Image::Magick stub specifically enables the module to load and create objects; actual image operations require a future Java backend (e.g., via javax.imageio).

Test plan

• make passes (all unit tests)
• use Image::Magick loads without error
• Image::Magick->new creates objects
• eval { require Image::Magick } works for optional dependency checks
• jcpan Image::Magick reports "up to date"
• jcpan -t Image::Magick tests run (fail on missing backend, not on load)

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