vpm.tools: add parse functions to handle module updates

[ttytm]

One of the last changes to vpm before moving to working on the cmd_vpm2 repo. It's also the most complicated of the outstanding changes.

It adds parsing to the update command to improve evaluation of updatable modules. E.g. it,

• fixes potential recursive loops with shared dependencies - currently it can happen when:

  v install https://gitlab.com/tobealive/a
  # below cause unintended recursive loops
  v install https://gitlab.com/tobealive/a # reinstall
  v update https://gitlab.com/tobealive/a # a module specific update with rec. deps
  v update # a full update if a module with rec. deps is installed
  

• improves detection of new modules to install when dependencies have changed.

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TODO:

• implement parsing urls of updatable hg modules
• add hg update test
• add recursive dependency test

copilot:summary

copilot:walkthrough