Add regression test for IVM resetting the encoding context

[popematt]

Issue #, if available:

fix #1020

Description of changes:

When investigating #1020, I discovered that it was already fixed by #940 (but that change had not yet been released). That PR added test cases for the conformance test runner, but the issue also existed (and was also fixed) for non-conformance-test use cases. Before closing #1020, I want to add the reproduction from the issue so that if we ever update/replace the conformance tests, we don't lose the test coverage for this case.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

❌ Patch coverage is 80.95238% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.00%. Comparing base (96d4ff5) to head (3395fab).

Files with missing lines	Patch %	Lines
src/lazy/reader.rs	80.95%	0 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1022      +/-   ##
==========================================
+ Coverage   78.97%   79.00%   +0.02%     
==========================================
  Files         140      140              
  Lines       34822    34843      +21     
  Branches    34822    34843      +21     
==========================================
+ Hits        27502    27526      +24     
+ Misses       5245     5238       -7     
- Partials     2075     2079       +4     

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