Build tags for smaller binaries that don't need net/http or encoding/json

[ldemailly]

Discovered through the excellent https://github.com/Zxilly/go-size-analyzer that
even without any logging of http, binaries included vendor/golang.org/x/net/http/httpproxy

it's because of net/http's init and the linker not being smart enough to elide that:

httpproxy.FromEnvironment().ProxyFunc() is called by envProxyFunc
envProxyFunc is called by http.ProxyFromEnvironment (already an exported function)
http.ProxyFromEnvironment is called while setting up http.DefaultTransport, which is an exported package variable

(credit @CarsonHoffman for the analysis)

Also for the records,

go list  -tags whichevertags -f '{{.ImportPath}}: {{.Deps}}' ./...

lets you see dependencies (which go mod why doesn't)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (c4c7d64) to head (a085108).
Report is 2 commits behind head on main.

❗ Current head a085108 differs from pull request most recent head 7ec8cc2

Please upload reports for the commit 7ec8cc2 to get more accurate results.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #63   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            4         6    +2     
  Lines          550       612   +62     
=========================================
+ Hits           550       612   +62     

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[ldemailly]

Didn't readily figure out how to get codecov read the coverage*.out but gave up for now - also fortio/workflows#2 (comment) might have to bite the bullet on the token thing as the coverage action keeps silently failing

But this is good to go now (I think) and will propagate in fortio/cli (main objective for small binaries) and fortio/scli

[ccoVeille]

LGTM 👍