Read default registry configuration at construction

[Shubham-Padkonde]

Registry() currently uses a Config() created when the module is imported. Setting SPECTATOR_OUTPUT_LOCATION or process tags after import therefore has no effect on a new default registry. For example, selecting memory still produces a socket writer.

Create the default configuration when the registry is constructed. Explicit configuration objects retain their existing behavior. Two regression tests cover environment changes after import and between registry instances; both fail before the fix.

Validation: all 122 tests pass on Linux, including UDP and Unix socket tests. Pylint rates the changed files 10/10, and mypy with the Linux platform passes for all 56 source files. The test run reports existing resource warnings for a file and socket.