[plenarius]

Sets PORTED_FROM = "v4.13.0", and the corpus parity line in python/README.md.

Corpus parity on the game's 32,832 models was run on #110's branch (a17214f), which is the code main now has; this PR changes only two strings.

• decompile: 25,597 binary models identical; Go and Python give the same warnings and notes on all of them, and on the 342 merged haks models;
• parse: 7,235 ASCII models identical, and the mutations identical or refused by both;
• compile: 32,832 identical, and the same as cleanmodels compile --cli.

On merged main (42f71b3), go test ./... and the three fixture parity scripts pass.

Release notes draft: ~/dev/nwn/nwmain-analysis/release-notes-v4.13.0.md.