style: cleanup code by golangci-lint

[Dreamacro]

As described in #775, boxo requires a better static code analysis tool since the currently used ipdxco/unified-github-workflows has limitation capabilities.

Therefore, I am attempting to use golangci-lint here (while retaining the original ipdxco/unified-github-workflows). I have disabled all golangci-lint default configurations and enabled some checks that I find particularly valuable.

golangci-lint config

linters:
  disable-all: true
  enable:
    - gci
    - gofumpt
    - gosimple
    - govet
    - ineffassign
    - misspell
    - staticcheck
    - unconvert
    - unused
    - usestdlibvars

issue:
  exclude-files:
    - ".*\\.pb\\.go"

After performing the lint fixes, boxo generally has the following issues:

1. Some files have imported package names divided into groups without any discernible pattern (if there is one, please let me know), and gci can fix this.
   for example:
   

   boxo/ipld/unixfs/io/dagreader_test.go

   Lines 3 to 15 in 8ca0ca2

   	import (
   	"bytes"
   	"io"
   	"strings"
   	"testing"
   	mdag "github.com/ipfs/boxo/ipld/merkledag"
   	"github.com/ipfs/boxo/ipld/unixfs"
   	context "context"
   	testu "github.com/ipfs/boxo/ipld/unixfs/test"
   	)

2. many unnecessary type conversions can be detected and fixed using unconvert.
3. Other minor issues, such as unnecessary blank lines, octal notation, statements that will never be executed, etc.

There might be some other valuable plugins, such as unused, and I would like to hear your opinions on them.

[codecov]

Codecov Report

Attention: Patch coverage is 77.14286% with 8 lines in your changes missing coverage. Please review.

Project coverage is 60.49%. Comparing base (9d04741) to head (c591403).

Files with missing lines	Patch %	Lines
gateway/serve_http_content.go	25.00%	1 Missing and 2 partials ⚠️
files/util.go	66.66%	1 Missing ⚠️
filestore/fsrefstore.go	0.00%	1 Missing ⚠️
gateway/backend_car_files.go	0.00%	1 Missing ⚠️
ipld/unixfs/unixfs.go	0.00%	1 Missing ⚠️
routing/http/types/json/responses.go	50.00%	1 Missing ⚠️

@@            Coverage Diff             @@
##             main     #797      +/-   ##
==========================================
+ Coverage   60.47%   60.49%   +0.02%     
==========================================
  Files         244      244              
  Lines       31102    31101       -1     
==========================================
+ Hits        18809    18816       +7     
+ Misses      10616    10610       -6     
+ Partials     1677     1675       -2     

Files with missing lines	Coverage Δ
bitswap/bitswap.go	69.13% <ø> (ø)
bitswap/client/internal/getter/getter.go	81.81% <ø> (ø)
bitswap/client/internal/peermanager/peermanager.go	91.85% <ø> (ø)
...wap/client/internal/peermanager/peerwantmanager.go	88.50% <ø> (-0.04%)	⬇️
...tswap/client/internal/session/sessionwantsender.go	96.83% <ø> (+0.24%)	⬆️
...l/sessioninterestmanager/sessioninterestmanager.go	100.00% <ø> (ø)
...p/client/internal/sessionmanager/sessionmanager.go	100.00% <ø> (ø)
.../internal/sessionpeermanager/sessionpeermanager.go	100.00% <ø> (ø)
bitswap/client/wantlist/wantlist.go	90.47% <ø> (ø)
bitswap/message/message.go	83.15% <100.00%> (-0.72%)	⬇️
... and 64 more

... and 5 files with indirect coverage changes

[lidel]

Triage notes

• thank you @Dreamacro – parking for now as we are unsure if we want to manually add this to every go repo
• @galargh thoughts if this could/should be part of Unified CI for GO instead?

[hsanjuan]

We could merge the fixes without the CI changes for now?

[Dreamacro]

@hsanjuan I'll revert the CI changes later.

[Dreamacro]

done

[galargh]

go-check from uci uses govet and staticcheck. I think the addition of extra linters listed here to the common workflow should be evaluated individually:

- gci
- gofumpt
- gosimple
- ineffassign
- misspell
- unconvert
- unused
- usestdlibvars

It might be also worth considering making golangci-lint workflow part of the go-check, and exposing the linter selection to the workflow users.

One thing that I think we should keep in mind during that process is the quality of the local development iteration. We definitely want some level of static checking of the code, but we also don't want the checks to negatively impact the contribution experience.