Security: Update dependencies to fix CVE-2025-63811 in jose2go

## Summary
Security vulnerability CVE-2025-63811 in transitive dependency jose2go (via gosnowflake → 99designs/keyring) requires updating to jose2go v1.8.0.

## Vulnerability Details
- **CVE:** CVE-2025-63811
- **Package:** github.com/dvsekhvalnov/jose2go
- **Affected Versions:** v1.5.0 through v1.7.0
- **Severity:** Medium (DoS)
- **Type:** Denial of Service via JWT bomb attack

## Dependency Chain
```
vault-plugin-database-snowflake
└─ github.com/snowflakedb/gosnowflake
└─ github.com/99designs/keyring
└─ github.com/dvsekhvalnov/jose2go v1.5.0 (VULNERABLE)
```

## Attack Vector
An attacker can craft malicious JSON Web Encryption (JWE) tokens with exceptionally high compression ratios, causing memory exhaustion and denial of service when processed.

## Fix Available
A pull request has been submitted to 99designs/keyring to update jose2go from v1.5.0 to v1.8.0:
- **keyring PR:** https://github.com/99designs/keyring/pull/141
- **gosnowflake Issue:** https://github.com/snowflakedb/gosnowflake/issues/1630

## Recommended Actions
1. Monitor the keyring PR for merge
2. Monitor gosnowflake for dependency update
3. Once gosnowflake releases with the patched keyring, update vault-plugin-database-snowflake's dependency
4. Update `go.mod` to require the patched gosnowflake version

## Testing
The jose2go v1.8.0 update has been tested with keyring and is fully backward compatible:
- ✅ No breaking changes
- ✅ All encryption/decryption operations work identically
- ✅ All tests pass

## References
- CVE Details: https://www.mail-archive.com/debian-bugs-dist@lists.debian.org/msg2068478.html
- JWT Bomb Issue: https://github.com/dvsekhvalnov/jose2go/issues/33
- Debian Security: Bug#1120701
- jose2go v1.8.0 Release: https://github.com/dvsekhvalnov/jose2go/tree/v1.8.0

## Impact
This vulnerability affects all HashiCorp Vault deployments using the Snowflake database plugin, which is used for:
- Snowflake database secret management
- Dynamic credential generation for Snowflake
- Vault-managed Snowflake authentication

## Priority
Medium - While the impact is DoS (not data breach), the fix is simple with no breaking changes, making it low-risk to apply once available upstream.