Rearrange span processors to avoid repeating scrubbing and other tweaking

[alexmojaki]

Previously every span processor was wrapped in MainSpanProcessorWrapper which does various things including scrubbing which is quite slow. This meant that computation was inefficiently repeated for each processor. By default there are two such processors, one for the console and one for sending to logfire, so the computation was doubled. This PR bundles each processor into a SynchronousMultiSpanProcessor which simply delegates to each of them, and that is wrapped in a MainSpanProcessorWrapper to prevent the computation duplication. The same is done for PendingSpanProcessor. All this means that this code:

import logfire

logfire.configure()

with logfire.span('outer'):
    for _ in range(1000):
        with logfire.span('inner'):
            pass

runs about 30-40% faster.

TailSamplingProcessor has also been moved up in the tree of processors and is only created once instead of multiple times, which saves on computation and memory and prevents creating pending spans for spans that have already finished.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (7e6b140) to head (2d0b0c0).
Report is 1 commits behind head on main.

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Files          137       137           
  Lines        10920     10929    +9     
  Branches      1520      1524    +4     
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+ Hits         10920     10929    +9     

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