Add zstd support

[vearutop]

No description provided.

[github-actions]

Lines Of Code

Language	Files	Lines	Code	Comments	Blanks	Complexity	Bytes
Go	3 (+1)	608 (+47)	400 (+35)	90 (+4)	118 (+8)	112 (+8)	13.9K (+1K)
Go (test)	5 (+1)	551 (+85)	412 (+62)	8	131 (+23)	23	14.2K (+2.2K)
Markdown	4	193 (+1)	142 (+1)	0	51	0	6.7K (+58B)

[github-actions]

Unit Test Coverage

total: (statements) 84.1%
changed lines: (statements) 79.4%, coverage is less than 90.0%, consider testing the changes more thoroughly

Coverage of changed lines

File	Function	Coverage
Total		79.4%
server.go		81.8%
server.go:139	encodeFile	84.6%
server.go:119	encodeFiles	80.0%
zstd/encoding.go		75.0%
zstd/encoding.go:15	AddEncoding	84.6%

Coverage diff with base branch

File	Function	Base Coverage	Current Coverage
Total		85.1%	84.1% (-1.0%)
server.go	encodeFile	no function	82.4%
server.go	encodeFiles	84.0%	77.8% (-6.2%)
zstd/encoding.go	AddEncoding	no function	75.0%

[Copilot]

Copilot reviewed 7 out of 8 changed files in this pull request and generated no comments.

Files not reviewed (1)

• go.mod: Language not supported

Comments suppressed due to low confidence (1)

server_test.go:303

• [nitpick] The use of a hard-coded Etag value may lead to brittle tests if the underlying zstd compression changes. Consider deriving the expected Etag from the file content or the encoder output to improve test resilience.

assert.Equal(t, "1bp69hxb9nd93.zst", rw.Header().Get("Etag"))

[github-actions]

Go API Changes

# github.com/vearutop/statigz/zstd
## compatible changes
package added

# summary
Inferred base version: v1.4.3
Suggested version: v1.5.0

[github-actions]

Benchmark Result

Benchmark diff with base branch

name                old time/op    new time/op    delta
Server_ServeHTTP-4    3.58µs ± 2%    3.58µs ± 1%   ~     (p=1.000 n=5+5)

name                old alloc/op   new alloc/op   delta
Server_ServeHTTP-4    7.35kB ± 0%    7.35kB ± 0%   ~     (all equal)

name                old allocs/op  new allocs/op  delta
Server_ServeHTTP-4      19.0 ± 0%      19.0 ± 0%   ~     (all equal)

Benchmark result

name                time/op
Server_ServeHTTP-4  3.58µs ± 1%

name                alloc/op
Server_ServeHTTP-4  7.35kB ± 0%

name                allocs/op
Server_ServeHTTP-4    19.0 ± 0%