Add documentation for new public key callback functions

[devin-ai-integration]

Added documentation for 14 new callback functions in chapter06.md:

• DH Callbacks:

  • wolfSSL_CTX_SetDhGenerateKeyPair
  • wolfSSL_CTX_SetDhAgreeCb

• Ed25519 Callbacks:

  • wolfSSL_CTX_SetEd25519SignCb
  • wolfSSL_CTX_SetEd25519VerifyCb

• X25519 Callbacks:

  • wolfSSL_CTX_SetX25519KeyGenCb
  • wolfSSL_CTX_SetX25519SharedSecretCb

• Ed448 Callbacks:

  • wolfSSL_CTX_SetEd448SignCb
  • wolfSSL_CTX_SetEd448VerifyCb

• X448 Callbacks:

  • wolfSSL_CTX_SetX448KeyGenCb
  • wolfSSL_CTX_SetX448SharedSecretCb

• RSA PSS Callbacks:

  • wolfSSL_CTX_SetRsaSignCheckCb
  • wolfSSL_CTX_SetRsaPssSignCb
  • wolfSSL_CTX_SetRsaPssVerifyCb
  • wolfSSL_CTX_SetRsaPssSignCheckCb

The documentation includes function prototypes, registration methods, context setting functions, build requirements, and references to example implementations.

Link to Devin run: https://app.devin.ai/sessions/a8cbc63f14f049db85bf9d8679008f12
Requested by: Anthony

[devin-ai-integration]

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[anhu]

Looks good to me.

[dgarske]

Please fix for the other algorithms also, ED25519, X448 and RSA PSS.