fix: correctly parse i128::MIN from text Ion

[almann]

The text Ion parser rejected i128::MIN (-170141183460469231731687303715884105728) as out of range, even though it is a valid i128 value. This happened because the parser stripped the sign, parsed the magnitude as i128, then negated. Since the magnitude of i128::MIN is i128::MAX + 1, parsing it as i128 failed.

Fixed by parsing the magnitude as u128 with proper range validation, then using wrapping_neg() to correctly convert to the negative i128 value.

Added boundary value tests for i32, i64, and i128 min/max values.

Add read_ints_overflow test to verify the parser correctly rejects integers outside the i128 range:

• i128::MAX + 1 (positive overflow)
• i128::MIN - 1 (negative overflow)

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 94.23077% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.36%. Comparing base (bbcd84c) to head (aa2cc4c).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lazy/text/matched.rs	94.23%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1018      +/-   ##
==========================================
+ Coverage   78.33%   78.36%   +0.02%     
==========================================
  Files         138      138              
  Lines       34188    34232      +44     
  Branches    34188    34232      +44     
==========================================
+ Hits        26781    26825      +44     
+ Misses       5345     5344       -1     
- Partials     2062     2063       +1     

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