add Bitgesell coin parameters

[newmattock]

Summary:
Adds Bitgesell mainnet and testnet coin definitions to ElectrumX.

Related bounty or issue:
BitgesellOfficial/bitgesell#81

What changed:

• Adds Bitgesell and BitgesellTestnet coin classes with mainnet/testnet genesis hashes, address prefixes, WIF bytes, xpub/xprv bytes, RPC ports, and SegWit deserialization.
• Uses parameters from BitgesellOfficial/bitgesell Core chainparams.
• Adds focused tests that verify the new coin classes are discoverable and match the Core parameters.

Validation:

• PYTHONPYCACHEPREFIX=/private/tmp/bitgesell-pycache python3 -m py_compile electrumx/lib/coins.py tests/lib/test_bitgesell_coin.py
• PYTHONDONTWRITEBYTECODE=1 /private/tmp/electrumx-bitgesell-venv/bin/python -m pytest tests/lib/test_bitgesell_coin.py -q (2 passed)
• PYTHONDONTWRITEBYTECODE=1 /private/tmp/electrumx-bitgesell-venv/bin/python -m pytest tests/lib/test_coins.py -q (16 passed)
• git diff --check

Notes:
I did not run the full suite because this local environment was only provisioned with the dependencies needed for the coin tests.

[MyTH-zyxeon]

Review-assist note for the Bitgesell spesmilo#81 improvement lane.

I checked the public PR metadata and diff. This is a focused ElectrumX integration patch:

• adds Bitgesell and BitgesellTestnet coin classes in electrumx/lib/coins.py
• wires mainnet/testnet lookup coverage through tests/lib/test_bitgesell_coin.py
• uses SegWit deserialization, BGL/TBGL shortnames, address/WIF version bytes, RPC ports, and genesis/hash-count constants
• keeps the change contained to coin registration plus tests, with no wallet, signing, RPC credential, or live-chain behavior in this review note

Suggested maintainer checks before merge:

• confirm the Bitgesell mainnet genesis hash, address prefixes, WIF byte, and RPC port against the current Core/client constants
• confirm whether BitgesellTestnet should intentionally inherit the mainnet GENESIS_HASH, or whether testnet should define a distinct genesis hash
• run the new pytest coverage together with the existing coin lookup tests
• if ElectrumX expects TX_COUNT / TX_COUNT_HEIGHT to be periodically refreshed, confirm these are acceptable seed values rather than acceptance blockers

From the public patch shape, this looks like a useful low-risk ElectrumX enablement candidate for the spesmilo#81 improvement queue. I did not run tests, start ElectrumX, connect to a node, use wallet keys, submit payment details, or perform any live-chain action for this review-assist note.