Add KDF parameter customization and builder module refactor

[coreyleavitt]

Summary

KDF Parameter Customization

KDBX4 (Argon2):

• argon2_iterations - get/set time cost
• argon2_memory - get/set memory cost (KiB)
• argon2_parallelism - get/set thread count
• argon2_variant - get/set variant (argon2id or argon2d)

KDBX3 (AES-KDF):

• transform_rounds - get/set AES transformation rounds

Database Creation Rewrite

• Rewrite create_database() to build KDBX structure from scratch instead of copying a template file
• Remove blank_database.kdbx template (no longer needed)
• Fresh cryptographic seeds generated for each new database (addresses security concern in issue [Security vulnerability] Seeds are not changed on database save libkeepass/pykeepass#219)
• Add KDBX3 database creation support via version=3 parameter

Builder Module

Extract database creation logic into kdbx_parsing/builder.py with type-safe API:

• Argon2Config dataclass with .standard(), .high_security(), .fast() presets
• AesKdfConfig dataclass with .standard(), .high_security() presets
• Cipher enum (AES256, CHACHA20, TWOFISH)
• KdfAlgorithm enum (ARGON2ID, ARGON2D, AES_KDF)

Other Changes

• Bump minimum Python version to 3.11 (for StrEnum support)
• Add 18 new tests

Example Usage

from pykeepass import PyKeePass, create_database, Argon2Config, AesKdfConfig, Cipher

# KDBX4 with default settings
kp = create_database('vault.kdbx', password='secret')

# KDBX4 with high security Argon2
kp = create_database('vault.kdbx', password='secret', kdf=Argon2Config.high_security())

# KDBX4 with custom Argon2 parameters
kp = create_database('vault.kdbx', password='secret', 
                     kdf=Argon2Config(iterations=100, memory_kib=262144, parallelism=4))

# KDBX3 database with AES-KDF
kp = create_database('legacy.kdbx', password='secret', version=3)
kp = create_database('legacy.kdbx', password='secret', version=3, 
                     kdf=AesKdfConfig(rounds=100000))

# Modify KDF on existing KDBX4 database
kp = PyKeePass('vault.kdbx', password='secret')
kp.argon2_iterations = 50
kp.argon2_memory = 131072
kp.argon2_variant = 'argon2d'
kp.save()

# Modify KDF on existing KDBX3 database
kp = PyKeePass('legacy.kdbx', password='secret')
kp.transform_rounds = 100000
kp.save()

Test Plan

• All 142 tests pass
• CI passes on Python 3.11, 3.12, 3.13