feat: implement IK custom dictionary support

[anonymous-404404]

Task Description

Solution Description

Passed Regressions

Upgrade Compatibility

Other Information

Release Note

[CLAassistant]

All committers have signed the CLA.

[LINxiansheng]

Document AI & IK Custom Dictionary Score

Document AI Functions Score
===========================
score: 0.00 / 100
load_file: 0 / 50
ai_split_document: 0 / 50

IK Custom Dictionary Score
==========================
score: 100.00 / 100
ik_custom_dict: 100 / 100

FTS Large Benchmark Score

FTS Large Benchmark Score
=========================
score: 0.00 / 100
mean_improvement: -178.51%
full_score_improvement: 50.00%

build_improvement: -321.74%
  build_ik_all_sec: baseline=35.2836, current=186.297, improvement=-428.00%
  build_ik_content_sec: baseline=28.3764, current=180.543, improvement=-536.24%
  build_beng_en_sec: baseline=14.7578, current=14.904, improvement=-0.99%
tokenize_improvement: 4.95%
  tokenize_ik_avg_ms: baseline=0.76478, current=0.7204, improvement=5.80%
  tokenize_beng_avg_ms: baseline=0.42262, current=0.4053, improvement=4.10%
query_improvement: -218.74%
  query_cn_avg_ms: baseline=16.6628, current=130.573, improvement=-683.62%
  query_beng_avg_ms: baseline=24.3042, current=24.2897, improvement=0.06%
  query_mixed_avg_ms: baseline=17.5593, current=31.4559, improvement=-79.14%
  query_limit_avg_ms: baseline=16.2334, current=34.4552, improvement=-112.25%

FTS Large Benchmark Report

========================================
FTS Large Benchmark Report
========================================
timestamp:              2026-07-17 09:36:37
label:                  vldb-ci-29567374757-2
git_head:               6190bf4
git_dirty:              0
rows:                   20000
batch:                  500
rounds:                 3000
query_rounds:           200
samples:                3
warmup:                 30
skip_load:              0
----------------------------------------
select1_avg_ms:         0.2017
select1_stdev_ms:       0.0016
raw_load_sec:           1.467
raw_load_rows_per_sec:  13633.3
build_ik_all_sec:       186.297
build_ik_content_sec:   180.543
build_beng_en_sec:      14.904
build_total_sec:        381.757
----------------------------------------
tokenize_ik_avg_ms:     0.7204
tokenize_ik_median_ms:  0.7205
tokenize_ik_stdev_ms:   0.0008
tokenize_beng_avg_ms:   0.4053
tokenize_beng_median_ms:0.4042
tokenize_beng_stdev_ms: 0.0023
----------------------------------------
query_cn_hits:          20000
query_cn_avg_ms:        130.5735
query_cn_stdev_ms:      0.0151
query_beng_hits:        11000
query_beng_avg_ms:      24.2897
query_beng_stdev_ms:    0.0039
query_mixed_hits:       9998
query_mixed_avg_ms:     31.4559
query_mixed_stdev_ms:   0.0101
query_limit_hits:       20
query_limit_avg_ms:     34.4552
query_limit_stdev_ms:   0.0271
========================================

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