Encode basicConstraints critical flag and pathlen into generated CSRs

[cconlon]

Description

ReqCertFromX509() previously did not copy basicConstCrit, pathLen, or pathLenSet from the WOLFSSL_X509 into the Cert, so a basicConstraints extension added to an X509_REQ lost its critical flag and pathlen when the CSR was signed. The certificate path (CertFromX509()) already copied these fields.

openssl req -text output for a CSR with basicConstraints added as critical, CA:TRUE, pathlen:1, shows this before/after this fix:

Before:

X509v3 Basic Constraints:
    CA:TRUE

After:

X509v3 Basic Constraints: critical
    CA:TRUE, pathlen:1

Reported in wolfSSL/wolfssljni#368.

Testing

Adds unit test test_x509_ReqCertFromX509_ext_critical, which fails without this fix.

Checklist

• added tests
• updated/added doxygen
• updated appropriate READMEs
• Updated manual and documentation

[Copilot]

Pull request overview

This PR fixes CSR generation so a basicConstraints extension added to an X509_REQ preserves its critical flag and pathLen when the CSR is signed, aligning request behavior with the existing certificate path (CertFromX509()).

Changes:

• Update ReqCertFromX509() to copy basicConstCrit, pathLen, and pathLenSet from the request into the generated Cert.
• Add a unit test that builds a CSR with basicConstraints: critical, CA:TRUE, pathlen:1 and verifies these fields round-trip through DER parsing.
• Register the new unit test in the X.509 API test declarations.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
tests/api/test_x509.h	Registers the new CSR basicConstraints critical/pathLen unit test.
tests/api/test_x509.c	Adds test_x509_ReqCertFromX509_ext_critical() to validate DER encoding round-trip for critical + pathLen.
src/x509.c	Copies basicConstraints critical/pathLen fields from request into Cert during CSR signing.

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[github-actions]

MemBrowse Memory Report

gcc-arm-cortex-m4-openssl-compat

• FLASH: .text +128 B (+0.0%, 771,540 B / 1,048,576 B, total: 74% used)
  No memory changes detected for:
• gcc-arm-cortex-m0plus
• gcc-arm-cortex-m3
• gcc-arm-cortex-m4
• gcc-arm-cortex-m4-baremetal
• gcc-arm-cortex-m4-crypto-only
• gcc-arm-cortex-m4-dtls13
• gcc-arm-cortex-m4-min-ecc
• gcc-arm-cortex-m4-pkcs7
• gcc-arm-cortex-m4-pq
• gcc-arm-cortex-m4-rsa-only
• gcc-arm-cortex-m4-sp-math
• gcc-arm-cortex-m4-tls12
• gcc-arm-cortex-m4-tls13
• gcc-arm-cortex-m7
• gcc-arm-cortex-m7-pq
• gcc-arm-cortex-m7-tls13
• linuxkm-pie
• linuxkm-standard
• stm32-sim-stm32h753