Fix stacking transaction cookies

[tusharpandey13]

Fixes: #1917

Overview

The original logout handler (handleLogout) only deleted the session cookie, leaving transaction cookies behind.
This caused potential accumulation of transaction state cookies (__txn_{state}) for users, particularly those who were unauthenticated or experienced interrupted login flows.

Changes

• Modified AuthClient.handleLogout to actively clear all transaction cookies (matching the transaction store's cookie prefix)
• Added a public getter method getCookiePrefix to TransactionStore
• Added test file redundant-txn-cookie-deletion.test.ts to test this specific flow.
• Some linting changes.

Tests

PASSING

Usage

No change in contract

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.25%. Comparing base (1ef1862) to head (af84ca0).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2077      +/-   ##
==========================================
+ Coverage   82.05%   82.25%   +0.19%     
==========================================
  Files          21       21              
  Lines        1967     1989      +22     
  Branches      343      348       +5     
==========================================
+ Hits         1614     1636      +22     
  Misses        347      347              
  Partials        6        6              

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