fix GenerateJwe

[Ac-Kevin]

PR Description: Fix critical encoding/writer issues

1. GZIP footer loss: Fixed by explicitly closing gzip.Writer before reading the buffer to ensure footer (checksum/length) is written.
2. Base64 padding: Replaced base64.URLEncoding with RawURLEncoding to omit padding (=) for standards-compliant URL-safe strings (e.g., JWT tokens).
3. PSS salt length: Set rsa.PSSSaltLengthEqualsHash to enforce salt length matching hash size (RFC 8017 compliance), avoiding cross-implementation inconsistencies from PSSSaltLengthAuto.

Each fix aligns with spec requirements and prevents data corruption/parsing errors.

Verified JWE Data Generation: After implementing the fixes.