feat: add new function to calculate storage unit expiry timestamp

[sanjayprabhu]

Why is this change needed?

Expose a function that calculates the expiry timestamp from just the block timestamp.

Merge Checklist

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PR-Codex overview

This PR focuses on updating the @farcaster/core and @farcaster/hub-nodejs packages to version 0.18.6 and 0.15.6 respectively, along with introducing a new function for calculating storage unit expiry timestamps.

Detailed summary

• Updated @farcaster/core to version 0.18.6.
• Updated @farcaster/hub-nodejs to version 0.15.6.
• Added getStorageExpiryTimestampFromBlockTimestamp function in limits.ts.
• Modified getStorageUnitExpiry to use the new expiry function.
• Added tests for getStorageExpiryTimestampFromBlockTimestamp in limits.test.ts.

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[changeset-bot]

⚠️ No Changeset found

Latest commit: e8b911a

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 14.52%. Comparing base (1880070) to head (e8b911a).
⚠️ Report is 555 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/core/src/limits.ts	85.71%	1 Missing ⚠️

❌ Your project status has failed because the head coverage (14.52%) is below the target coverage (70.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2645       +/-   ##
===========================================
- Coverage   74.05%   14.52%   -59.54%     
===========================================
  Files          99       62       -37     
  Lines        9425    19170     +9745     
  Branches     2097     8159     +6062     
===========================================
- Hits         6980     2785     -4195     
- Misses       2327    13501    +11174     
- Partials      118     2884     +2766     

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