Fix JA4 number of cipher suites and extensions (#19)

JA4 specification[^1] mentions that the numbers of cipher suites and
of extensions should be limited to two characters and that if the
values are over 99 we should output 99.

That value should never be reached, but it may happen on the
Internet. I discovered the bug while implementing stricter JA4 parsing
in [IVRE](https://github.com/ivre/ivre)[^2] and parsing logs from
fingerproxy. Turns out, at least one (testing) tool[^3] produces a
wrong fingerprint with the current implementation:
`t12d1120600_e33c72313a64_a1e935682795` (112 extensions) rather than
`t12d990600_e33c72313a64_a1e935682795`.

The JA4_a part of the wrong fingerprint is 11 characters and IVRE now
fails to parse it. This simple patch fixes the issue.

[^1]: See [technical details](https://github.com/FoxIO-LLC/ja4/blob/main/technical_details/JA4.md#number-of-ciphers).
[^2]: Change: [ff696af5](ivre/ivre@ff696af#diff-f7cabf3913e3ffe5d6cb6b7b0b2832170b265d64c03cbad89f93c94c0286a076).
[^3]: Namely [TLS tester](https://testssl.sh/dev/).

pkg/ja4/types.go

@@ -29,8 +29,8 @@ func (x tlsVersion) String() string {
 	}
 	return "00"
 }
-func (x numberOfCipherSuites) String() string { return fmt.Sprintf("%02d", x) }
-func (x numberOfExtensions) String() string   { return fmt.Sprintf("%02d", x) }
+func (x numberOfCipherSuites) String() string { return fmt.Sprintf("%02d", min(x, 99)) }
+func (x numberOfExtensions) String() string   { return fmt.Sprintf("%02d", min(x, 99)) }
 func (x cipherSuites) String() string         { return joinUint16(x, cipherSuitesSeparator) }
 func (x extensions) String() string           { return joinUint16(x, extensionsSeparator) }
 func (x signatureAlgorithms) String() string  { return joinUint16(x, signatureAlgorithmSeparator) }