Avoid deep copy of numpy buffers on unspill

[crusaderky]

• Linting blocked by version bump; pre-commit bump #75
• Closes Deep copy causes memory flare on unspill distributed#7407
• Must be merged together with Avoid deep copy of numpy buffers on unspill distributed#7435

Note that, with this PR, distributed 2022.01.1 will be backwards compatible with zict 2.2.0, but distributed 2022.12.1 won't work with zict 2.3.0. There is precedent for this; the consensus in the previous instance was that this should not be an issue for most users.

Benchmark

import gc
import numpy
import zict
from distributed.spill import SpillBuffer

print(zict.__version__)
a = numpy.random.random(512 * 2**20 // 8)
buf = SpillBuffer("/tmp", target=1)
buf["xxx"] = a
buf.slow.cache.clear()  # Clear weakref cache
buf["xxx"]
buf.get_metrics()

Output:

2.2.0
{...
 'unpickle_time_total': 0.07338492600138125}

2.3.0
{...
 'unpickle_time_total': 0.00016480999875057023}

[mrocklin]

No objection to this or the related PR in distributed. Feel free to merge at will.