Internalize cryptobyte package

[hslatman]

No description provided.

[Copilot]

Pull request overview

This PR vendors (internalizes) the cryptobyte package into internal/cryptobyte and updates the legacy X.509 parser to use the internal copy, removing the module dependency on golang.org/x/crypto.

Changes:

• Replaced golang.org/x/crypto/cryptobyte imports with github.com/smallstep/pkcs7/internal/cryptobyte in the legacy X.509 parser.
• Added an internal copy of cryptobyte (including ASN.1 helpers) plus upstream tests and licensing files.
• Removed the golang.org/x/crypto requirement from go.mod (and cleared go.sum accordingly).

Reviewed changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
internal/legacy/x509/parser.go	Switches legacy X.509 parsing to use the internal cryptobyte copy.
internal/cryptobyte/doc.go	Documents why cryptobyte is internalized and scoped to legacy parsing support.
internal/cryptobyte/string.go	Adds cryptobyte.String parsing helpers.
internal/cryptobyte/builder.go	Adds cryptobyte.Builder construction helpers.
internal/cryptobyte/asn1.go	Adds ASN.1 parsing/building helpers for cryptobyte.
internal/cryptobyte/asn1/asn1.go	Adds ASN.1 tag/type constants used by cryptobyte.
internal/cryptobyte/cryptobyte_test.go	Adds upstream tests for Builder/String behavior.
internal/cryptobyte/asn1_test.go	Adds upstream tests for ASN.1 helpers.
internal/cryptobyte/LICENSE	Adds upstream license for the copied code.
internal/cryptobyte/PATENTS	Adds upstream patents grant for the copied code.
go.mod	Drops the golang.org/x/crypto dependency.
go.sum	Cleared due to dependency removal.

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