Fix ActivationRegistry scope handling and ActivationFn deserialization panic

[Copilot]

Fixes two bugs in src/activation.rs related to NeuronScope::NONE handling and unsafe deserialization behavior, plus corrects get_random_connection to take &self instead of &mut self.

Changes

• src/neuralnet.rs: Changed get_random_connection receiver from &mut self to &self since it only reads from the network.

• src/activation.rs: Fixed activations_in_scope to return an empty Vec when scope == NeuronScope::NONE, instead of returning all activations. Also added a guard to filter out activations whose own scope is NONE from all scope queries. Previously, since NeuronScope::NONE has no bits set, every bitflags contains check would return true, causing activations_in_scope(NeuronScope::NONE) to incorrectly return all registered activations.

• src/activation.rs: Fixed ActivationFn::deserialize to return Err(serde::de::Error::custom(...)) instead of calling panic! when the activation function name is not found in the registry. Panicking inside Deserialize allows malformed or untrusted input to crash consumers; serde expects a D::Error to be returned instead.

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[HyperCodec]

bruh you did the wrong thing

[HyperCodec]

@copilot I intended for you to work on the following part of the thread:

• ActivationRegistry::activations_in_scope uses a.scope.contains(scope) without handling scope == NeuronScope::NONE. Because every bitflags value contains NONE (0 bits), calling activations_in_scope(NeuronScope::NONE) will currently return all activations, contradicting the documented meaning of NONE (“will not be randomly placed anywhere”).
  Fix: explicitly return an empty vec for scope == NeuronScope::NONE, or add a guard in the filter (e.g., scope != NONE && a.scope != NONE && a.scope.contains(scope)).
  src/activation.rs:206

• ActivationFn deserialization panics when an activation name is missing (panic!("Activation function {name} not found")). Panicking inside Deserialize makes malformed/untrusted input able to crash consumers; serde expects this to return a D::Error instead.
  Fix: replace the panic with Err(serde::de::Error::custom(...)) (and avoid unwrap() by using ok_or_else).

just add those changes to this PR.

[Copilot]

@copilot I intended for you to work on the following part of the thread:

• ActivationRegistry::activations_in_scope uses a.scope.contains(scope) without handling scope == NeuronScope::NONE. Because...

Done in commit 4777194:

• activations_in_scope now returns an empty Vec when scope == NeuronScope::NONE, and also filters out activations whose own scope is NONE
• ActivationFn::deserialize now returns Err(serde::de::Error::custom(...)) instead of panicking when the activation name isn't found