docs: call the factory precompile B20Factory, not IB20Factory (#1631)

IB20Factory is the Solidity interface; the deployed singleton precompile
is B20Factory. Rename the two prose references that called the precompile
itself "IB20Factory", matching the existing PolicyRegistry /
ActivationRegistry naming convention in the same doc.

Generated with Claude Code

Co-authored-by: Claude <noreply@anthropic.com>

Author: stevieraykatz

docs/base-chain/specs/upgrades/beryl/b20.mdx

@@ -14,7 +14,7 @@ B20 supports two variants:
 
 ## ERC-20 Compatibility
 
-B20 tokens are implemented as **Rust precompiles** rather than EVM smart contracts, making them faster, cheaper, and more native to the chain. All tokens are deployed via the singleton `IB20Factory` precompile.
+B20 tokens are implemented as **Rust precompiles** rather than EVM smart contracts, making them faster, cheaper, and more native to the chain. All tokens are deployed via the singleton B20Factory precompile.
 
 <Check>
 B20 implements the full ERC-20 standard surface with complete selector parity - it is a drop-in replacement for existing tooling and integrations.
@@ -168,7 +168,7 @@ B20 implements ERC-2612 (signed approvals) using an EIP-712 domain shaped as `(n
 
 ## Factory
 
-All B20 tokens are created through the singleton `IB20Factory` precompile via `createB20(variant, salt, params, initCalls)`.
+All B20 tokens are created through the singleton B20Factory precompile via `createB20(variant, salt, params, initCalls)`.
 
 | Parameter | Description |
 |-----------|-------------|