Adds LazyRawTextReader support for reading IVMs

[zslayton]

Builds on outstanding PRs #609, #612, #613, #614, #616, #617, and #619.

Adds support for reading Ion version markers (IVMs) to the LazyRawTextReader.

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: 46.08% and project coverage change: -0.54% ⚠️

Comparison is base (998a5bf) 81.65% compared to head (cc2bef2) 81.11%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #620      +/-   ##
==========================================
- Coverage   81.65%   81.11%   -0.54%     
==========================================
  Files         122      123       +1     
  Lines       22235    22570     +335     
  Branches    22235    22570     +335     
==========================================
+ Hits        18155    18308     +153     
- Misses       2411     2574     +163     
- Partials     1669     1688      +19     

Files Changed	Coverage Δ
src/lazy/decoder.rs	60.00% <ø> (ø)
src/lazy/system_reader.rs	77.15% <0.00%> (ø)
src/lazy/text/matched.rs	67.32% <ø> (ø)
src/lazy/text/raw/sequence.rs	53.27% <0.00%> (ø)
src/lazy/text/raw/struct.rs	68.57% <0.00%> (ø)
src/lazy/any_encoding.rs	40.98% <40.98%> (ø)
src/lazy/binary/raw/sequence.rs	60.00% <66.66%> (-0.94%)	⬇️
src/lazy/binary/raw/struct.rs	60.86% <66.66%> (-1.36%)	⬇️
src/lazy/text/buffer.rs	87.63% <72.54%> (-0.63%)	⬇️
src/lazy/text/raw/reader.rs	90.40% <83.33%> (+0.11%)	⬆️
... and 1 more

... and 1 file with indirect coverage changes

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[popematt]

Here's another test case to consider.

Suggested change

	mismatch_ivm("$ion__1_0");
	mismatch_ivm("$ion__1_0");
	mismatch_ivm("$ion_1_0_0");