Replace broad `except Exception` that can silently drop eICR data

[nickclyde]

Problem

Two core processors wrap large blocks in bare except Exception (both do call logger.exception, so tracebacks are logged — but the granularity hides real failures):

1. packages/text-to-code/.../eicr_processor.py:47-76 — the try wraps the entire nested node/sub-xpath loop. A single malformed sub-node aborts extraction for the whole (base_xpath, data_field) and returns whatever was collected so far. Early returns here could be masking systematic extraction failures.
2. packages/text-to-code/.../schematron_processor.py:74-123 — per-validationResult try/except … continue. Line 92 (assertion_id_elem.text.strip()) assumes assertionID exists; when it doesn't, the resulting AttributeError is swallowed and the error is silently dropped.

Proposed scope

• Narrow the try in get_text_candidates to per-sub-node so one bad node doesn't kill the batch; catch specific exceptions (etree.XPathError, AttributeError, ValueError).
• In schematron_processor, guard assertion_id_elem is None explicitly (like the other *_elem None checks at :83-89) instead of relying on the broad except; narrow the catch.
• Add a metric/structured-log counter distinguishing "no candidates (expected)" from "extraction raised" so the passthrough investigation has signal.

Acceptance criteria

• Tests cover: malformed sub-node mid-loop (other candidates still returned); a validationResult missing assertionID (handled deterministically, logged, not crashed).
• No bare except Exception remains in these two functions.