fix(transport): get oid_type on local transport by weihanglo · Pull Request #7229 · libgit2/libgit2

Exercise git_remote_oid_type on a SHA256 local transport.

The after-disconnect assertion is commented out because
local_oid_type dereferences `t->repo`, which local_close
has already freed (SIGSEGV).

I ran these commands to test btw:

```
cmake .. -DGIT_EXPERIMENTAL_SHA256=ON -DBUILD_TESTS=ON
cmake --build .
./libgit2_tests -snetwork::remote::local::sha256_oid_type
```

Cache `oid_type` in `transport_local` struct during `connect()`
so `git_remote_oid_type()` keeps working after disconnect.

This matches the smart transport behavior.