Forward ignore_extra to nested checked types in CheckedPMap.create

[lntutor]

Fixes #326

Description

CheckedPMap.create(..., ignore_extra=True) does not forward ignore_extra to the nested checked key/value CheckedType.create calls. As a result, extra fields in a nested checked value (e.g. a PRecord) still raise even though ignore_extra=True was requested. CheckedPVector / CheckedPSet thread ignore_extra correctly (via the _checked_type_create helper); CheckedPMap was the one collection that dropped it.

from pyrsistent import CheckedPMap, PRecord, field

class Rec(PRecord):
    a = field()

class M(CheckedPMap):
    __key_type__ = str
    __value_type__ = Rec

M.create({"k": {"a": 1, "extra": 2}}, ignore_extra=True)
# before: AttributeError: 'extra' is not among the specified fields for Rec
# after:  M({'k': Rec(a=1)})

Root cause

In CheckedPMap.create (pyrsistent/_checked_types.py), the nested checked_key_type.create(key) and checked_value_type.create(value) calls omitted ignore_extra=ignore_extra. The sibling helper _checked_type_create (used by CheckedPVector/CheckedPSet) already forwards it.

Fix

Pass ignore_extra=ignore_extra to both nested create calls. Both CheckedType.create (the abstract base signature) and PRecord.create accept ignore_extra, so forwarding is safe for every valid key/value type.

Added tests

In tests/checked_map_test.py, mirroring the existing ignore_extra patterns in tests/record_test.py:

• test_create_forwards_ignore_extra_to_value — the exact case from the issue (value type is a PRecord).
• test_create_without_ignore_extra_still_raises_for_value — the default (ignore_extra=False) still raises.
• test_create_forwards_ignore_extra_to_nested_checked_value — value type is a CheckedPVector of records, so ignore_extra has to be forwarded all the way down.

The two positive tests fail on the unpatched code and pass with the fix. Full suite: pytest tests/ → 640 passed, 1 skipped (also verified with PYRSISTENT_NO_C_EXTENSION=1).

Note: the fix also forwards ignore_extra on the key-create path for symmetry with the value path and with _checked_type_create. That path is not separately unit-tested because a record's source data is a dict (unhashable), so it cannot appear as a map key in practice; the meaningful, user-facing path is the value one covered above.