Feature/xslt declarations and call template

[frankarensmeier]

Summary

This PR merges the full feature/xslt-declarations-and-call-template branch.

It substantially improves XSLT conformance by:

• parsing and loading more top-level XSLT declarations
• adding runtime support for globals, named templates, and parameter validation
• improving scoping and focus handling across templates and XPath declarations
• implementing mode runtime semantics including mode="#current"
• adding xsl:document lowering
• fixing namespace-sensitive XML construction, xsl:namespace-alias, and kind-test behavior
• improving XSLT runner wiring for initial template/mode and XML assertions

Highlights

• Full declaration parsing instead of early aborts on many unsupported declarations
• Better global xsl:variable / xsl:param execution and named-template support
• Correct XSLT error handling for required params
• Lexical scope fixes across XSLT and shared XPath lowering
• Built-in template behavior driven by xsl:mode metadata
• Namespace-aware element/attribute construction and aliasing
• Prefix-independent kind-test matching
• assert-xml normalization improvements in the conformance runner

Implementation Notes

Key files:

• xee-xslt-ast/src/ast_core.rs
• xee-xslt-ast/src/instruction.rs
• xee-xslt-compiler/src/ast_ir.rs
• xee-ir/src/declaration_compiler.rs
• xee-ir/src/function_compiler.rs
• xee-interpreter/src/interpreter/interpret.rs
• xee-interpreter/src/xml/kind_test.rs
• xee-testrunner/src/testcase/xslt.rs
• xee-testrunner/src/testcase/assert.rs

Validation

• Filtered XSLT conformance check passes
• Filter baseline increased to 2890 passing tests
• Multiple targeted conformance clusters fixed along the way, including mode/runtime, document-node, namespace-alias, and kind-test regressions

[gronke]

I'm exploring xee as a pure-Rust XSLT backend and have been validating this branch against our own transforms.
It builds cleanly and the XSLT compiler suite passes for us, and it already covers named templates, call-template with parameters, global variables, modes, and document() — a big step forward.
Happy to help this land: I can test it against real-world stylesheets and review in smaller chunks if that is useful.

One gap I've hit for a browser/WebAssembly target: load_stylesheet (for xsl:import/xsl:include) and the document() fallback read through std::fs, so imports cannot resolve without a filesystem.
Would you be open to a pluggable in-memory URI/stylesheet resolver, so a host can feed documents and imported stylesheets from a map? Happy to contribute that on top of this branch.