fix(font): restore font query and shaping compatibility

[kiennq]

Issue

query-font is currently a placeholder that always returns nil, so Lisp callers cannot retrieve the font name, file, metrics, or OpenType capability from a resolved font object. font-shape-gstring also incorrectly requires its second argument to be an integer, while GNU callers pass optional values such as nil or symbols.

Solution

• Implement query-font for font objects using the existing font-info and runtime font metric paths.
• Return GNU-compatible name, file, pixel size, width, ascent, descent, spacing, and capability slots.
• Preserve GNU-compatible font-object type errors for invalid inputs.
• Stop imposing an incorrect fixnum requirement on font-shape-gstring's optional shaping argument.
• Add focused font query and bytecode dispatch regressions.

Verification

• cargo test -p neovm-core --lib query_font_eval_returns_metrics_with_terminal_frame_selected -- --nocapture passes.
• cargo test -p neovm-core --lib vm_font_stub_tail_uses_direct_dispatch -- --nocapture passes.
• cargo check -p neovm-core passes.
• cargo fmt --all -- --check passes.
• git diff --check upstream/main...HEAD passes.
• Windows validation temporarily applied the separate Unix-signal gating from fix(windows): gate Unix signal handlers #276; that change is not included in this PR.

[Copilot]

🟢 Approval recommended

The new query-font mapping was verified against the documented GNU contract and helper layouts, the font-shape-gstring fix is correct, and the changes are well-covered by updated tests with no issues found.

Pull request overview

This PR restores GNU-compatible behavior for two font primitives in neovm-core. Previously query-font was a placeholder that always returned nil, preventing Lisp callers from retrieving a resolved font's name, file, metrics, and OpenType capabilities. It also corrects font-shape-gstring, which wrongly rejected non-integer values for its optional shaping/direction argument that GNU callers legitimately pass as nil or symbols. The real query-font now reuses the existing font-info entity-probe and runtime-font metric paths, and is relocated from the pure-dispatch symbols module to the context-aware font module.

Changes:

• Implement a real builtin_query_font in font.rs that returns the GNU 9-slot vector (name, file, pixel size, max width, ascent, descent, space width, average width, capability) and preserves the font-object wrong-type error for invalid inputs.
• Remove the incorrect expect_fixnum validation on font-shape-gstring's second argument, and re-point the query-font registration to the new implementation.
• Add focused regressions (query-font metrics on a terminal frame, plus the bytecode direct-dispatch update) and drop the now-obsolete pure-dispatch placeholder test.

File summaries

File	Description
neovm-core/src/emacs_core/font.rs	Adds builtin_query_font, mapping the internal font-info vector to GNU's query-font slots with correct type/error handling.
neovm-core/src/emacs_core/builtins/symbols.rs	Removes the old placeholder builtin_query_font that always returned nil.
neovm-core/src/emacs_core/builtins/mod.rs	Re-points the query-font subr registration to the new context-aware implementation.
neovm-core/src/emacs_core/builtins/stubs.rs	Drops the incorrect fixnum requirement on font-shape-gstring's optional argument.
neovm-core/src/emacs_core/font_test.rs	Adds a query-font regression covering metrics extraction and the wrong-type error path.
neovm-core/src/emacs_core/bytecode/vm_test.rs	Updates the direct-dispatch test to call font-shape-gstring with nil.
neovm-core/src/emacs_core/builtins/tests.rs	Removes the obsolete pure-dispatch query-font placeholder assertion and renames the test.

Review details

• Files reviewed: 7/7 changed files
• Comments generated: 0
• Review effort level: Balanced

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