Tech debt: Refactor oversized modules

[evans-sam]

Problem

Three source files are significantly oversized:

• src/wsdl/index.ts — 1,464 LOC
• src/wsdl/elements.ts — 1,198 LOC
• src/client.ts — 633 LOC

Combined, these three files hold almost all of the complexity in the library.

Why it matters

• Hard to reason about end-to-end; boundaries between concerns are implicit.
• Hard to test in isolation (reinforces Security: Add OSSF Scorecard workflow and README badge #17).
• Hard for LLM-assisted edits and reviews.
• Makes the strict-mode migration (Security: Add dependency vulnerability scan in CI #15) harder than it needs to be.

Proposed approach

This is a multi-PR effort. Suggested sequence:

Phase 1 — client.ts (smallest, clearest wins):

• Extract request-builder into src/client/request-builder.ts.
• Extract response-parser into src/client/response-parser.ts.
• Extract event-wiring / EventEmitter surface into src/client/events.ts.
• Keep client.ts as the public facade.

Phase 2 — src/wsdl/elements.ts:

• Each "element" class is roughly independent. Split into a directory with one file per element class (or small related groups).
• Keep a barrel src/wsdl/elements/index.ts.

Phase 3 — src/wsdl/index.ts:

• After elements are split, the WSDL parser can be broken into:
  • schema loader
  • schema cache
  • XML ingestion (sax wiring)
  • tree builder
• Land each as its own PR.

Each phase: tests pass, public API unchanged.

Acceptance criteria

• No source file exceeds ~500 LOC.
• Public API (exports) unchanged.
• All tests pass.
• Internal module boundaries are clearer (no circular deps).