Add measured offsets for Linux and Mac Mono builds

Attaching to a Mono game on Linux or Mac reads no build identity right now: there''s no equivalent of the PE debug GUID lookup, so those platforms always go through version detection. The ELF and Mach-O offsets tables also have `None` for the members the collection readers need, so dictionaries and hashsets never resolve there even when detection works.

Same plan as the PE builds:

- read the ELF build-id and Mach-O UUID at attach, and report unknown builds like PE attaches do
- key measured builds per format (the PE key is a 16-byte GUID, an ELF build-id is 20 bytes)
- measure offsets from players built with [auto-splitting-test-fixtures](https://github.com/LiveSplit/auto-splitting-test-fixtures) and fill the table arms where two builds agree

I can run the Linux players; the Mac ones need someone with a Mac.

- [x] #155
- [x] #156

Start by reading the existing PE build-identity lookup and the ELF and Mach-O offsets tables, then inspect the players built with auto-splitting-test-fixtures. Implement build-ID and UUID reporting, key measured builds by their format-specific identifiers, and fill table entries only where measurements agree; verify Linux players and arrange Mac validation.

Written by the indexing model from the issue text.