Isolate configuration defaults

[ydah]

What? Why?

Gruf::Configuration#reset assigns default values directly from VALID_CONFIG_KEYS. Although the outer hash is frozen, mutable defaults such as services, server_options, and nested RPC server options remain shared.

Controllers::Base.bind appends service classes to Gruf.services, which mutates the shared default array. As a result, calling Gruf.reset reuses the polluted array, causing services to accumulate across tests and development reloads.

This uses Active Support's deep_dup when applying defaults during reset, ensuring each reset receives independent mutable objects while preserving the existing configuration key structure.

How was it tested?

• Added regression specs for mutable configuration defaults