trace: encode non-finite floats in auto telemetry JSON

[immanuwell]

Fixes a tiny footgun in auto trace telemetry.

When an auto span has a float attribute like math.Inf(1), json.Marshal rejects it. autoSpan.end ignored that error, so the emitted span buffer was nil. Kinda bad: the span just disappears.

Repro on origin/main:

WithAttributes(attribute.Float64("inf", math.Inf(1)))

A focused test fails with span data was dropped.

This PR encodes non-finite doubles as protobuf JSON strings: NaN, Infinity, -Infinity, and decodes them too.

Checked:

go test ./... # in trace/
make precommit

[dashpole]

This comes up when using opentelemetry-go-instrumentation, right? Can you open a bug describing how you encountered this?

[codecov]

Codecov Report

❌ Patch coverage is 80.64516% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.9%. Comparing base (15063b2) to head (4b16e07).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
trace/internal/telemetry/number.go	77.7%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #8364   +/-   ##
=====================================
  Coverage   82.9%   82.9%           
=====================================
  Files        314     314           
  Lines      25087   25114   +27     
=====================================
+ Hits       20801   20826   +25     
+ Misses      3912    3910    -2     
- Partials     374     378    +4     

Files with missing lines	Coverage Δ
trace/internal/telemetry/value.go	65.0% <100.0%> (+0.8%)	⬆️
trace/internal/telemetry/number.go	57.6% <77.7%> (+17.0%)	⬆️

... and 1 file with indirect coverage changes

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