Allow logging to a recording without first calling rr.init()

[jleibs]

What

Our recording functions would always check the global recording state even though they could validly operate just on a manually-created recording.

With this change, this becomes valid:

import rerun as rr

rec = rr.new_recording("rerun_example_cube_flat")

rec.log("points", rr.Points3D([1, 2, 3]))

rec.save("output.rrd")

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