Add Freezable for asset compliance support

[Jesse-Sawa]

Summary

• Add Freezable abstract contract for account freezing
• Add IFreezable interface
• Add FreezableToken example demonstrating asset compliance pattern
• Update README with Asset Compliance documentation

Test plan

• Contracts compile successfully
• Manual review of Freezable integration pattern

---

Note

Medium Risk
Introduces new role-gated freezing/unfreezing logic and ERC-7201 storage layout intended for integration into asset contracts; misuse or misconfiguration of roles could block transfers or break upgrade safety.

Overview
Adds Asset Compliance support via a new Freezable abstract contract + IFreezable interface, providing role-based freeze/unfreeze (single and batch), isFrozen, and internal revert helpers using an ERC-7201 namespaced storage slot.

Includes a new FreezableToken example that blocks transfers when sender/recipient is frozen, plus a Foundry test suite covering transfer behavior, access control, and event emission. Updates README.md to document the new Asset Compliance offering, interfaces, examples, and docs links.

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[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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Bugbot Autofix prepared a fix for the issue found in the latest run.

• ✅ Fixed: Missing virtual on unfreeze and unfreezeAccounts functions
  • Added the virtual keyword to both unfreeze and unfreezeAccounts functions to match the symmetric freeze and freezeAccounts functions.

Or push these changes by commenting:

@cursor push fa3f00f68d

Preview (fa3f00f68d)

diff --git a/src/Freezable.sol b/src/Freezable.sol
--- a/src/Freezable.sol
+++ b/src/Freezable.sol
@@ -63,12 +63,12 @@
     }
 
     /// @inheritdoc IFreezable
-    function unfreeze(address account) external onlyRole(FREEZE_MANAGER_ROLE) {
+    function unfreeze(address account) external virtual onlyRole(FREEZE_MANAGER_ROLE) {
         _unfreeze(_getFreezableStorageLocation(), account);
     }
 
     /// @inheritdoc IFreezable
-    function unfreezeAccounts(address[] calldata accounts) external onlyRole(FREEZE_MANAGER_ROLE) {
+    function unfreezeAccounts(address[] calldata accounts) external virtual onlyRole(FREEZE_MANAGER_ROLE) {
         FreezableStorageStruct storage $ = _getFreezableStorageLocation();
 
         for (uint256 i; i < accounts.length; ++i) {

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