[BUG] Introduce Bloom Filter in UIN existence check to reduce DB calls during generation

[dhanendra06]

Summary:
During bulk UIN generation, UinGeneratorImpl.generateId() calls uinService.uinExist() for every candidate UIN to check against previously assigned UIns. This results in one DB query per candidate, which
becomes a significant bottleneck as the assigned UIN pool grows into the millions.

Component: kernel-idgenerator-service
Files Affected:

• UinServiceImpl.java — uinExist() method
• UinGeneratorImpl.java — generateId() loop

Problem:
// UinGeneratorImpl.java:129 — DB hit on every loop iteration
if (uinFilterUtils.isValidId(generatedUIN) && !uinService.uinExist(generatedUIN)) {

// UinServiceImpl.java:144 — always goes to DB
public boolean uinExist(String uin) {
Optional uinEntityAssignedOptional = uinRepositoryAssigned.findById(uin);
return uinEntityAssignedOptional.isPresent();
}

Proposed Solution:
Introduce a BloomFilter (Guava, already transitively available) in UinServiceImpl:

1. On startup — populate the Bloom filter by loading all existing UIns from UinEntityAssigned
2. On uinExist() — check Bloom filter first:
   - Returns false → UIN is definitely new, skip DB query entirely
   - Returns true → confirm with DB (handles rare false positives)
3. On transferUin() — add newly assigned UIns to the Bloom filter to keep it in sync

Expected Benefit:

• Eliminates ~99.9% of DB existence checks during bulk UIN generation (at 0.1% false positive rate)
• ~120MB RAM for 100M UIns — acceptable for a long-running service
• No change needed in UinGeneratorImpl — logic stays encapsulated in uinExist()
• No new Maven dependency — Guava is already available via Spring Boot

Acceptance Criteria:

• Bloom filter initialized at startup from UinEntityAssigned table
• uinExist() checks Bloom filter before hitting DB
• Bloom filter updated whenever a UIN is transferred/assigned
• Unit test covering false positive path (Bloom says exists → DB confirms not exists → treated as new)
• Benchmark showing reduced DB call count during a generation run