fix: prevent processor from attempting to run an empty select_all

[prestwich]

Motivation

Processor was encountering a panic when running with only an ethereum remote

Message:  assertion failed: !ret.inner.is_empty()
Location: /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-util-0.3.21/src/future/select_all.rs:40

• the error occurs because futures_util::select_all is invoked with an empty vector.

• the only place where this could occur in our code is in NomadAgent::run_many which calls select_all on the result of an iterator

  • grep -ri --include="*.rs" "select_all" * will identify locations where select_all is invoked

• this iterator may only be empty if the names slice is empty when called

• NomadAgent::run_many is invoked from NomadAgent::run_all

• it is also invoked from <Processor as **NomadAgent>::run_all overriding the default trait impl

• the <Processor as NomadAgent>::run_all would run certain tasks ONLY for subsidized networks

• it would do this by loading the subsidized_networks and calculating the intersection with remote_networks, and making a task for each network in the intersection

• this would result in an empty task vector if no subsidized networks were specified in remote_networks

Solution

• Adds checks that replica is non-empty to the default implementations of NomadAgent::run_all and NomadAgent::run_many
• Add check that specified_subsidized is not empty when running select_all in <Processor as NomadAgent>::run_all
• Filter subsidized_remotes by inclusion in remote_networks to prevent similar errors in the future

PR Checklist

• Added Tests
• Updated Documentation
• Updated CHANGELOG.md for the appropriate package

[luketchang]

Can delete some redundant checks but other than that LGTM, thanks for fixing my bug