feat(dwarf): AddressRemap engine (#143 DWARF Phase 2 inc 3a)

[avrabe]

Summary

The mathematical core of DWARF address remapping. Composes the two anchors already released:

• v0.16.0 (inc 1): per-function base — component-provenance v2 code_range
• v0.17.0 (inc 2): intra-function InstrOffsetMap — LEB-drift tracking

into AddressRemap::translate(input_addr) -> Option<output_addr>: an input code-section-relative DWARF address → its fused-output address.

The three offset spaces (the whole game)

meld-core/src/dwarf.rs reconciles:

1. Input DWARF address — code-section-relative in the source component
2. Instruction-stream offset — relative to the first instruction (after the locals vector); what InstrOffsetMap keys on
3. Output DWARF address — merged function base + locals prefix + new instruction-stream offset

The locals-prefix length is identical input↔output (locals are preserved verbatim in the DWARF-remap path), so it cancels — recorded once per FunctionSpan.

Tests (6)

identity offsets · instruction-offset shift (LEB growth) · locals-prefix handling · multi-function selection via BTreeMap range lookup · miss cases (outside functions / mid-instruction / past end) · locals-prefix underflow guard

Scope

This is increment 3a — the engine. Increment 3b wires it into a gimli::write::Dwarf::from(convert_address) rewrite of the .debug_* sections behind a new DwarfHandling::Remap mode. gimli was added then removed in this PR to avoid shipping an unused dependency; it returns in 3b where it's actually used.

Test plan

• 6 new dwarf::tests green
• 301 lib tests green, clippy + fmt clean
• CI green

🤖 Generated with Claude Code

[github-actions]

LS-N verification gate

⚠️ 35/37 verified — 2 missing regression tests

	count
Passed (≥1 test, all green)	35
Failed (≥1 test failure)	0
Missing (no ls_*_NN_* test found)	2

_{Approved loss-scenarios.yaml entries are expected to have a
regression test named ls_<letter>_<num>_* (e.g. LS-A-11 →
ls_a_11_*). The gate runs each prefix via cargo test --lib --no-fail-fast and aggregates pass/fail/missing.}

Failed LS entries

(none)

Missing regression tests

• LS-R-13
• LS-M-6

_{Updated automatically by tools/post_verification_comment.py.
Source of truth: safety/stpa/loss-scenarios.yaml.}