Comparative Analysis of Efficacy Between Laparoscopic Subtotal Colectomy with Cecorectal Counterclockwise Isoperistaltic Anastomosis and Anterior-to-Posterior Inversion Isoperistaltic Anastomosis for Slow Transit Constipation

INTERVENTION: Counterclockwise Isoperistaltic Anastomosis (cecum rotated 180° counterclockwise and anastomosed with rectum in a peristaltic direction):Counterclockwise Isoperistaltic Anastomosis;Anterior‐to‐Posterior Inversion Isoperistaltic Anastomosis (inverted 180° from anterior to posterior and anastomosed with rectum in a peristaltic direction):Anterior‐to‐Posterior Inversion Isoperistaltic Anastomosis; CONDITION: Slow Transit Constipation PRIMARY OUTCOME: Gastrointestinal Quality of Life Index (GIQLI); SECONDARY OUTCOME: Wexner Constipation Score;Abdominal Pain Frequency Score;Abdominal Bloating Frequency Score;Wexner Incontinence Score;Time to First Flatus After Surgery;Time to First Defecation After Surgery;Postoperative Length of Hospital Stay;Operative Time;Intraoperative Blood Loss;Postoperative Complications and Adverse Events; INCLUSION CRITERIA: 1.Participants must meet the Rome IV diagnostic criteria for functional constipation. 2.Colonic transit testing must show a marker retention rate of >= 80% at 72 hours, confirming prolonged whole‐colon transit time. 3.Participants must have severe constipation refractory to standardized conservative treatment, meeting all of the following criteria: Wexner Constipation Score >= 15 and bowel movement frequency <= 2 times per week, accompanied by at least one of the following symptoms for > 6 months: straining during defecation, sensation of incomplete evacuation, or manual maneuvers to facilitate defecation. After at least 3 months of standardized medical treatment, including dietary fiber supplementation, osmotic laxatives, prokinetic agents, or pelvic floor biofeedback, the Wexner Constipation Score must have decreased by < 3 points or the Patient Global Impression of Improvement (PGI‐I) score must be >= 4, indicating “no change” or “worse.”; 4.Participa