Auto-resolve overloaded service pyspec files in pyAnalyzeLaurel

[joehendrix]

Summary

When verifying Python programs that use overloaded service clients,
users currently must manually specify a --pyspec flag for every
service module the program touches. This is tedious and error-prone,
especially as programs grow.

This PR integrates the resolveOverloads AST walker (added in the
previous commit) into pyAnalyzeLaurel so that when --dispatch files
are provided, the command automatically discovers which
.pyspec.st.ion files are needed and loads them—eliminating the need
for manual --pyspec flags in the common case.

Details

• Auto-resolution of pyspec files. After building the dispatch
  overload table, pyAnalyzeLaurel now walks the Python AST with
  resolveOverloads to collect the set of service modules actually
  used. For each resolved module, it derives the pyspec path relative
  to the dispatch file's directory and checks that the file exists on
  disk. Auto-resolved files that are not found are skipped with a
  warning on stderr, since the program may reference services for
  which no spec has been written yet. In contrast, files explicitly
  provided via --pyspec or --dispatch still produce a hard error
  if they are missing or unreadable, since an explicit flag implies
  the user expects the file to exist.
• Shared readDispatchOverloads helper. The dispatch-file-reading
  loop (read DDM, extract overloads, print warnings, merge tables) was
  duplicated between pyAnalyzeLaurelCommand and
  pyResolveOverloadsCommand. Both now call a single
  readDispatchOverloads function, reducing duplication and ensuring
  consistent error handling.
• extractStmtsFromProgram helper. Small utility that encapsulates
  toPyCommands + unwrapModule for extracting top-level Python
  statements from a Strata program.
• Backward compatibility. Explicit --pyspec flags continue to
  work unchanged; they are appended after auto-resolved paths so that
  user-specified specs always take effect.

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