Add vectorcall dispatch in vectorcall_type to check each type's
own slots.vectorcall before falling back to PyType::call.
Only dispatch when slots.call is None, to avoid misinterpreting
callable-instance vectorcalls (e.g. vectorcall_function) as
constructor vectorcalls.

Clear vectorcall when __init__ or __new__ is overridden in
update_slot to ensure subclass correctness.

Implement per-type vectorcall for 12 builtin types:
- Pattern A (skip args.clone): dict, set, list, bytearray
- Pattern B (skip dispatch): int, float, str, bool, tuple,
  frozenset, bytes, complex

Pattern B vectorcall functions now call through zelf.slots.new
instead of calling PyXxx::slot_new directly. This ensures Rust-level
subclasses with custom slot_new (e.g. stat_result subclassing tuple)
get their own constructor called correctly.

Fix PyStatResult::slot_new to use struct_sequence_new for proper
length validation and hidden field padding, matching structseq_new
behavior. Derive st_atime/st_mtime/st_ctime and their _ns variants
from integer time fields when not explicitly provided.