packages hierarchy should be a tree

[tharvik]

currently, the build graph is a tree, but the testing graph isn't

flowchart TD
    DC[discojs-core] --> |build| DN[discojs-node]
    DC --> |build| DW[discojs-web]
    DN --> |build & test| S[server]
    DW --> |build & test| W[web-client]
    DN --> |build| C[CLI]
    DN --> |test| DC
    S --> |test| DC

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that is quite cumbersome to know what is the origin of a bug, as when a test in discojs-core fails, the code one need to check is the union of discojs-core, discojs-node & server. it's also weird to need to build discojs-node to compile test for discojs-core.