Problems with `identity` in cpost configs

[reidsunderland]

While trying to migrate some v2 cpost configs to sr3 cpost, I came across some problems.

First problem:

The identity option isn't parsed correctly:

config option	parsed as sum=	result
sum d md5 on data	d	✅
sum n md5 on file name	n	✅
sum s sha512 on data	s	✅
identity md5name	m	❌ should be n md5 on file name
identity md5	m	❌ should be d md5 on file data
identity sha512	s	✅

Second problem:

When using sum n (md5name) with v03 format messages, identity is missing from the message:

{ "pubTime" : "20260129T174716.2993753", "baseUrl" : "sftp://localhost/", "relPath" : "tmp/test", "source" : "bunnymaster", "size" : "5", "atime" : "20260129T161256.87121107", "mtime" : "20260129T161246.786308", "mode" : "644" }

compared to v02 format messages:

Maybe this was intentional, because identity is optional in v03 messages and md5 on the file name is kind of useless? But the behaviour is inconsistent with the Python version and surprising/confusing.