Use worker threads for launching conda and windows registry when discovering

[karrtikr]

#21755

Spike results

Based on CPU profiles in #21755 (comment) discovery is mainly blocked by:

• Launching conda binary
• Launching REG binary for windows registry
• Windows Path discovery

Note spawning python binaries is fine, it blocks very little of the time.

[Tyriar]

@deepak1556 do you know why spawn would be blocking the thread for so long here?

Profiles at #21755 (comment)