Leaks in configatron.temp

Nobody has claimed this yet.

We've faced an issue with `configatron.temp` due to unexpected side effect
```ruby
# config changes in rspec case
# leaked into other
configatron.temp do
#leaks
configs.each { |config| configatron.origins[config.origin_id] = { app_id: '123' } }
# doesn't leak
# configatron.origins = configs.map { |cfg| [cfg.origin_id, { app_id: '123' }] }.to_h
example.run
end
```

After skimming through source code of `configatron.temp`, I humbly suggest authors to consider implementation of `configatron.temp` with `Marshal.dump` and `Marshal.load`, which looks like straightforward solution with rather strong guarantees.

Start by reading the source implementation of configatron.temp and reproduce the shown RSpec-style mutation case. Verify whether nested changes to configatron.origins persist after the block while reassignment does not. Define done as temporary configuration restoring all nested state without leaking into later examples, then assess the proposed Marshal approach against the existing behavior.

Written by the indexing model from the issue text.