feat: support algosdk 3.8 v41/42 block header fields (prev512, txn512, ld, ct)

feat: map rejectVersion when converting algod transactions to the indexer format

Co-authored-by: Cosimo Bassi <65770425+cusma@users.noreply.github.com>

Add a WalletConnect section stating that the SDK talks to the Pera
mobile app over WalletConnect v1 through the maintained
@perawallet/walletconnect client, that v2 is not supported, and that
sessions run on Pera-hosted bridges, so no WalletConnect Cloud project
ID is needed.

Replace the signData claim that the SDK "uses signBytes behind the
scenes"; the SDK never calls it. The wallet signs each item with the
"MX" prefix, exactly like algosdk.signBytes, so signatures verify with
algosdk.verifyBytes or verifySignature.

Refs #140, #149

When wc.perawallet.app/config.json is unreachable or lists no servers,
connect() fell back to https://bridge.walletconnect.org. WalletConnect
retired that host in 2023 and it no longer resolves, so every user who
reached the fallback got a QR code against a dead bridge and a hang.

Fall back to wallet-connect-fallback.perawallet.app instead, a
Pera-controlled DNS name that can be repointed at any bridge without an
SDK release. Precedence is unchanged: the dApp `bridge` option, then
config.json, then the fallback.

Refs #104

relates to #5

Docs: Clean up