Bug: `_IssueKind` is private/unexported but used in public `ValidationIssue.issue_kind` field

[Dog-Web]

Problem

ValidationIssue.issue_kind is typed as _IssueKind, a private enum that is not included in __all__ and not part of the public API:

# prompt_validation.py
class _IssueKind(enum.Enum):          # private name
    FAILED = "failed"
    NON_EXACT = "non_exact"

@dataclasses.dataclass(frozen=True)
class ValidationIssue:
    ...
    issue_kind: _IssueKind            # ← typed as private enum

__all__ exports ValidationIssue but not _IssueKind:

__all__ = [
    "PromptValidationLevel",
    "ValidationIssue",        # exported
    "ValidationReport",
    ...
]
# _IssueKind is NOT in __all__

This forces users to import a private symbol to filter individual issues:

from langextract.prompt_validation import _IssueKind  # accessing private!

report = validate_prompt_alignment(examples)
failed = [i for i in report.issues if i.issue_kind == _IssueKind.FAILED]

While ValidationReport.has_failed and ValidationReport.has_non_exact give aggregate info, users who need to categorize or filter individual issues have no public API to do so.

Proposed Fix

Rename _IssueKind → IssueKind (make it public) and add it to __all__. This is backwards-compatible for users relying on the public API.

class IssueKind(enum.Enum):
    FAILED = "failed"
    NON_EXACT = "non_exact"

__all__ = [
    "IssueKind",          # now exported
    "PromptValidationLevel",
    "ValidationIssue",
    ...
]

Users can then write clean, public-API-only code:

from langextract.prompt_validation import IssueKind

failed = [i for i in report.issues if i.issue_kind == IssueKind.FAILED]