Fix DKIM relaxed body canonicalization and optimize performance

This PR addresses critical issues in DKIM relaxed body canonicalization and modernizes the codebase by replacing GLib types with standard C types.

- **RFC Compliance**: Fixed incorrect canonicalization of lines containing only whitespace. Previously, such lines were not properly handled according to RFC 6376, which could lead to DKIM signature verification failures.
- **Memory Safety**: Fixed incorrect pointer dereference in `rspamd_dkim_skip_empty_lines` that could cause undefined behavior.

- **Zero-copy Optimization**: Reimplemented `rspamd_dkim_relaxed_body_step` to avoid unnecessary memory copies. The new implementation:
  - Processes input data directly without intermediate buffers
  - Reduces the number of `EVP_DigestUpdate` calls by processing larger chunks
  - Improves CPU cache efficiency
  - Results in significantly better performance for large email bodies

- Replaced all GLib types with standard C equivalents:
  - `gsize` → `size_t`
  - `gssize` → `ssize_t`
  - `gboolean` → `bool`
  - `TRUE/FALSE` → `true/false`
  - And other GLib-specific types
- Added necessary standard headers (`stdbool.h`, `stdint.h`, `limits.h`)

- Added comprehensive debug logging for:
  - Chunk processing with size information
  - Empty line detection and skipping
  - Space collapsing operations

Issue: #5590

src/libserver/dkim.h

@@ -20,6 +20,8 @@
 #include "contrib/libev/ev.h"
 #include "dns.h"
 #include "ref.h"
+#include <stdbool.h>
+#include <stdint.h>
 
 
 /* Main types and definitions */
@@ -126,7 +128,7 @@ struct rspamd_dkim_check_result {
 
 
 /* Err MUST be freed if it is not NULL, key is allocated by slice allocator */
-typedef void (*dkim_key_handler_f)(rspamd_dkim_key_t *key, gsize keylen,
+typedef void (*dkim_key_handler_f)(rspamd_dkim_key_t *key, size_t keylen,
 								   rspamd_dkim_context_t *ctx, gpointer ud, GError *err);
 
 /**
@@ -165,7 +167,7 @@ rspamd_dkim_sign_context_t *rspamd_create_dkim_sign_context(struct rspamd_task *
  * @param err
  * @return
  */
-rspamd_dkim_sign_key_t *rspamd_dkim_sign_key_load(const char *what, gsize len,
+rspamd_dkim_sign_key_t *rspamd_dkim_sign_key_load(const char *what, size_t len,
 												  enum rspamd_dkim_key_format type,
 												  GError **err);
 
@@ -174,8 +176,8 @@ rspamd_dkim_sign_key_t *rspamd_dkim_sign_key_load(const char *what, gsize len,
  * @param key
  * @return
 */
-gboolean rspamd_dkim_sign_key_maybe_invalidate(rspamd_dkim_sign_key_t *key,
-											   time_t mtime);
+bool rspamd_dkim_sign_key_maybe_invalidate(rspamd_dkim_sign_key_t *key,
+										   time_t mtime);
 
 /**
  * Make DNS request for specified context and obtain and parse key
@@ -184,10 +186,10 @@ gboolean rspamd_dkim_sign_key_maybe_invalidate(rspamd_dkim_sign_key_t *key,
  * @param s async session to make request
  * @return
  */
-gboolean rspamd_get_dkim_key(rspamd_dkim_context_t *ctx,
-							 struct rspamd_task *task,
-							 dkim_key_handler_f handler,
-							 gpointer ud);
+bool rspamd_get_dkim_key(rspamd_dkim_context_t *ctx,
+						 struct rspamd_task *task,
+						 dkim_key_handler_f handler,
+						 gpointer ud);
 
 /**
  * Check task for dkim context using dkim key
@@ -209,7 +211,7 @@ GString *rspamd_dkim_sign(struct rspamd_task *task,
 						  const char *selector,
 						  const char *domain,
 						  time_t expire,
-						  gsize len,
+						  size_t len,
 						  unsigned int idx,
 						  const char *arc_cv,
 						  rspamd_dkim_sign_context_t *ctx);
@@ -258,7 +260,7 @@ const unsigned char *rspamd_dkim_key_id(rspamd_dkim_key_t *key);
  * @param err
  * @return
  */
-rspamd_dkim_key_t *rspamd_dkim_parse_key(const char *txt, gsize *keylen,
+rspamd_dkim_key_t *rspamd_dkim_parse_key(const char *txt, size_t *keylen,
 										 GError **err);
 
 /**
@@ -269,10 +271,10 @@ rspamd_dkim_key_t *rspamd_dkim_parse_key(const char *txt, gsize *keylen,
  * @param outlen
  * @return
  */
-goffset rspamd_dkim_canonize_header_relaxed_str(const char *hname,
-												const char *hvalue,
-												char *out,
-												gsize outlen);
+off_t rspamd_dkim_canonize_header_relaxed_str(const char *hname,
+											  const char *hvalue,
+											  char *out,
+											  size_t outlen);
 
 /**
  * Checks public and private keys for match
@@ -281,9 +283,9 @@ goffset rspamd_dkim_canonize_header_relaxed_str(const char *hname,
  * @param err
  * @return
  */
-gboolean rspamd_dkim_match_keys(rspamd_dkim_key_t *pk,
-								rspamd_dkim_sign_key_t *sk,
-								GError **err);
+bool rspamd_dkim_match_keys(rspamd_dkim_key_t *pk,
+							rspamd_dkim_sign_key_t *sk,
+							GError **err);
 
 /**
  * Free DKIM key