Fix CodeQL call-graph edges dropped on (file, start_line) join miss (#25)

[rahlk]

Description

CodeQL-derived call-graph edges are joined back into Jedi's PyCallable
signature space by an exact (absolute_file_path, start_line) key. When
CodeQL and Jedi disagree on a definition's start line — most commonly
with decorated functions, where the two tools differ on whether the
def line or the first decorator line is the start — the caller lookup
missed and the entire edge was silently discarded (callee misses
degraded to ghost nodes). Jedi-derived edges, which are not
location-joined, were unaffected.

Fixes #25.

Steps to Reproduce

1. Analyze a project containing decorated functions/methods with CodeQL
   enabled (--codeql).
2. Inspect the call graph for edges whose caller is a decorated function.

Expected Behavior

The CodeQL-resolved edge is preserved even when the start line does not
match Jedi's.

Actual Behavior

The edge was dropped (caller miss) or weakened to a ghost node (callee
miss) with only a debug-level log line.

Fix

Replaced the exact-only location index with a resolution ladder:

1. exact (abs_path, start_line) — unchanged precise path;
2. on miss, candidates sharing (abs_path, short_name): a single
   candidate is taken directly, otherwise prefer those whose parameter
   count equals the CodeQL positional arity, then the nearest
   start_line;
3. no name match -> caller skipped / callee becomes a ghost (prior
   behavior).

The CodeQL query now emits Function.getName() and positional arity
(count(Function.getArg(_))) for both endpoints, with the callee bound
to a Function via calleeVal.getScope(). Jedi's parameter count
includes *args/**kwargs/keyword-only slots while CodeQL's arity is
positional only, so the arity filter is exact for plain signatures and
yields to the nearest-line tiebreak otherwise.

Testing

• Existing pytest suite: test_cli_help and test_single_file pass.
  test_cli_call_symbol_table_with_json fails on this machine due to a
  pre-existing, environment-dependent venv-build flake (No module named pip during xarray's editable install in core.py) — unrelated to
  this change (it runs with --no-codeql) and the subject of Decouple cache tiers: key the venv on dependency content, not directory existence #24.
• Live CodeQL analysis on the nested/decorated-method fixture: exit 0,
  produced a valid call graph with edges correctly carrying
  ["codeql","jedi"] provenance and resolving to proper PyCallable
  signatures (no spurious ghosts), confirming the new query columns and
  resolver work end-to-end.

Version

Patch bump 0.1.14 -> 0.1.15; CHANGELOG updated.