Property parsing had 4 classes of bug, all producing wrong addresses
for object property data:
1. Off-by-one in shortname skip: addr += 2*len missed the length byte
itself, causing property table scan to start 1 byte too early.
Affected get_prop_addr_len and get_next_property.
2. V3 property number slices bf[4:0] extracted 4 bits not 5.
Property numbers 16-31 were read as 0-15.
3. V3 property size slices bf[7:5] extracted 2 bits not 3.
Properties larger than 4 bytes got wrong sizes.
4. V5 property number/size slices bf[5:0] extracted 5 bits not 6.
Also fixed get_property_length reading size from the wrong byte in
V5 two-byte headers (was reading first byte which has property
number, instead of second byte which has size).
Root cause for all slice bugs: BitField uses Python [start:stop)
semantics but code was written as [high:low] inclusive notation.
Same class of bug as the write_global fix in commit e5329d6.
Adds comprehensive test coverage for three newly implemented Z-machine opcodes:
- op_test: Tests bitmap flag checking with all flags set, some missing, zero
flags, and identical values
- op_verify: Tests checksum verification with matching and mismatched checksums
- op_get_child: Tests getting first child of object with and without children
Also extends MockMemory with generate_checksum() and MockObjectParser with
get_child() to support the new tests.
ZStackBottom lacked attributes that normal stack operations need when
returning from a subroutine to the top level. Zork 1 hit this on the
first subroutine return during startup.
Copies the cleaned-up zvm source (ruff-compliant, ty-clean) back into
the zmachine module. Adds __init__.py with proper exports and updates
.gitignore for debug.log/disasm.log.
