fix(dwarf): adapt LineProgram::new to gimli 0.33 6-arg signature (#436 fallout) (#439)

Dependabot #436 bumped gimli 0.31→0.33, which inserted a `source_dir:
Option<LineString>` parameter into `LineProgram::new` (now 6 args:
working_dir, source_dir, source_file, source_file_info). Both emit call
sites still passed the 0.31 5-arg form, so main failed to compile
(E0061) — a semantic break that VCR-DBG-001 PR C's CI could not catch
because PR C branched before #436 and ran against the 0.31 lockfile, and
GitHub's merge is textual, not semantic.

Fix both call sites (the production emitter + the step-4 roundtrip test)
with source_dir = None (file sits in working_dir, matching prior
single-dir behaviour). The Writer trait / Address API is unchanged in
0.33, so the RelocWriter and relocation capture are unaffected.

Verified: workspace builds, clippy --all-targets clean, all 4
dwarf_debug_line_emit_394 oracles + the step-4 roundtrip green against
gimli 0.33.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: avrabe

crates/synth-core/src/dwarf_line.rs

@@ -206,10 +206,14 @@ pub fn emit_debug_sections(table: &[(u64, u32)], text_sym: usize) -> Vec<Emitted
     // high_pc one past the last mapped address.
     let high_pc = table.iter().map(|&(a, _)| a).max().unwrap_or(0) + 1;
 
+    // gimli 0.33 split the comp-dir/file args: (working_dir, source_dir,
+    // source_file, source_file_info). source_dir = None ⇒ the file sits in
+    // working_dir, matching the previous single-dir behaviour.
     let mut program = LineProgram::new(
         encoding,
         gimli::LineEncoding::default(),
         LineString::String(b"/synth".to_vec()),
+        None,
         LineString::String(b"synth.wasm".to_vec()),
         None,
     );

crates/synth-core/tests/dwarf_emit_roundtrip_step4.rs

@@ -88,10 +88,12 @@ fn emit_dwarf(table: &[(u64, u32)]) -> HashMap<String, Vec<u8>> {
         address_size: 4,
     };
     let mut dwarf = DwarfUnit::new(encoding);
+    // gimli 0.33: (working_dir, source_dir, source_file, source_file_info).
     let mut program = LineProgram::new(
         encoding,
         gimli::LineEncoding::default(),
         LineString::String(b"/synth".to_vec()),
+        None,
         LineString::String(b"dwarf_coherent.rs".to_vec()),
         None,
     );