encoding/asn1: use reflect.TypeAssert to improve performance

[apocelipes]

Use "reflect.TypeAssert" can gain some performance improvements:

goos: darwin
goarch: arm64
pkg: encoding/asn1
cpu: Apple M4
│ old │ new │
│ sec/op │ sec/op vs base │
ObjectIdentifierString-10 51.48n ± 1% 49.72n ± 2% -3.41% (p=0.000 n=10)
Marshal-10 7.549µ ± 0% 7.466µ ± 1% -1.10% (p=0.000 n=10)
Unmarshal-10 1.808µ ± 0% 1.798µ ± 0% -0.58% (p=0.000 n=10)
geomean 889.0n 873.8n -1.70%

 │ old │ new │ │ B/op │ B/op vs base │ 

ObjectIdentifierString-10 32.00 ± 0% 32.00 ± 0% ~ (p=1.000 n=10) ¹
Marshal-10 7.336Ki ± 0% 7.336Ki ± 0% ~ (p=1.000 n=10) ¹
Unmarshal-10 432.0 ± 0% 432.0 ± 0% ~ (p=1.000 n=10) ¹
geomean 470.0 470.0 +0.00%
¹ all samples are equal

 │ old │ new │ │ allocs/op │ allocs/op vs base │ 

ObjectIdentifierString-10 1.000 ± 0% 1.000 ± 0% ~ (p=1.000 n=10) ¹
Marshal-10 271.0 ± 0% 271.0 ± 0% ~ (p=1.000 n=10) ¹
Unmarshal-10 24.00 ± 0% 24.00 ± 0% ~ (p=1.000 n=10) ¹
geomean 18.67 18.67 +0.00%
¹ all samples are equal

Updates #62121

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Message from Carlana Johnson:

Patch Set 1:

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Patch Set 1:

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Message from kyose chang:

Patch Set 1:

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