simplify the Tracer interface by combining the TracerFor... methods

[marten-seemann]

No description provided.

[codecov]

Codecov Report

Merging #2671 into master will increase coverage by 0.06%.
The diff coverage is 87.50%.

@@            Coverage Diff             @@
##           master    #2671      +/-   ##
==========================================
+ Coverage   86.71%   86.76%   +0.06%     
==========================================
  Files         124      124              
  Lines        9862     9852      -10     
==========================================
- Hits         8551     8548       -3     
+ Misses        975      971       -4     
+ Partials      336      333       -3     

Impacted Files	Coverage Δ
server.go	84.57% <0.00%> (+0.89%)	⬆️
client.go	81.67% <100.00%> (ø)
logging/multiplex.go	94.87% <100.00%> (+2.01%)	⬆️
qlog/qlog.go	96.06% <100.00%> (+0.71%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ece3592...ee24d38. Read the comment docs.