feat: make initialize function public virtual (#5285)

### Description

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What's included in this PR?
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This PR makes the `initialize` function public and virtual to allow for
further overriding in derived contracts.
### Drive-by changes

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Are there any minor or drive-by changes also included?
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None.

### Related issues

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- Fixes #[issue number here]
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N/A.

### Backward compatibility

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Are these changes backward compatible? Are there any infrastructure
implications, e.g. changes that would prohibit deploying older commits
using this infra tooling?

Yes/No
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Yes
### Testing

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What kind of testing have these changes undergone?

None/Manual/Unit Tests
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N/A

---------

Co-authored-by: Yorke Rhodes <[email protected]>

.changeset/fast-comics-wave.md

@@ -0,0 +1,5 @@
+---
+"@hyperlane-xyz/core": patch
+---
+
+Make `initialize` function public virtual

solidity/contracts/token/HypERC20.sol

@@ -30,7 +30,7 @@ contract HypERC20 is ERC20Upgradeable, TokenRouter {
         address _hook,
         address _interchainSecurityModule,
         address _owner
-    ) external initializer {
+    ) public virtual initializer {
         // Initialize ERC20 metadata
         __ERC20_init(_name, _symbol);
         _mint(msg.sender, _totalSupply);