chore: remove v0.11.0–v0.12.1 Spark-repr migration notice

[jschoedl]

Summary

The temporary Spark-repr migration shim added in PR #1192 (April 2026) has reached its July 2026 expiry date. The in-code comment on _LEGACY_SPARK_REPR_RE explicitly says "remove after July 2026" — that date has passed (today is 2026-08-01).

What to remove

In datacontract/export/sql_type_converter.py:

1. The _LEGACY_SPARK_REPR_RE constant and its preceding comment (lines 11–13):

   # invalid physicalType from `import spark` in v0.11.0–v0.12.1 (#1048) (e.g. StringType() instead of string)
   # remove after July 2026
   _LEGACY_SPARK_REPR_RE = re.compile(r"^(?:[A-Z][a-zA-Z]*)?Type\(.*\)$")

2. The legacy-note branch inside _warn_cannot_map_type (lines 30–34):

   if isinstance(raw_type, str) and _LEGACY_SPARK_REPR_RE.match(raw_type):
       warning_message += (
           "\nNote: `datacontract import spark` emitted invalid physicalType values in v0.11.0–v0.12.1 (December 2025 until June 2026). "
           "Re-import datacontracts from these versions to fix."
       )

   Only remove this if block — the rest of _warn_cannot_map_type (the logger.warning call etc.) must stay.

3. The import re line at the top — but only if re is no longer used anywhere else in the file. Run grep -n '\bre\b' datacontract/export/sql_type_converter.py to verify before removing it.

Context

• Shim was introduced to help users who imported data contracts with versions v0.11.0–v0.12.1, which emitted invalid Spark physicalType values like StringType() instead of string.
• The shim appended a user-facing note to the "cannot map type" warning so affected users could re-import to fix their contracts.
• Enough time has passed (8+ months since v0.12.1) that the migration notice is no longer necessary.