Quarkchain: Root chain support POSW stake DecayByHeightAndTime

[ping-ke]

related issue: QuarkChain/pm#12

Added function and unit test for root chain to support PoSW stake decay to 50% after ENABLE_ROOT_POSW_STAKING_DECAY_TIMESTAMP
The enable time (ENABLE_ROOT_POSW_STAKING_DECAY_TIMESTAMP in config) currenlty set to 1746060000 which is 2025-05-01 08:40:00. And this can be changed if we finalize.

How to test:

1. Add related Unit test
2. Deploy pyquarkchain and goquarkchain with devnet config, run related test
   • integrate with UI (devnet.quarkchain.io);
   • integrate eth_api (Ethereum compatible RPC)
   • check posw has enable as expected, and decay as expected
   • use metamask to transfer token
   • use remix to deploy contract and call contract
   • use quarkchain public rpc (38391) to get chain/block/transaction info
   • check posw has enable as expected, and decay as expected