Fix simplifySingleMapSchema to generate named wrapper schemas

[lucy66hw]

Description

Rewrote simplifySingleMapSchema to create a { field: string, <type_name>: <value_schema> } wrapper instead of reconstructing/merging additional property definitions
Removed removeArrayOfMapWrapper (and its call sites) — array-of-map unwrapping no longer needed

###Test

message TermsAggregation {
  repeated SortOrderSingleMap order = 12;
}
message SortOrderSingleMap {

  // The path to a field or an array of paths. Some APIs support wildcards in the path, which allows you to select multiple fields.
  string field = 1;

  SortOrder sort_order = 2;
}

Issues Resolved

List any issues this PR will resolve, e.g. Closes [...].

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[codecov]

Codecov Report

❌ Patch coverage is 96.07843% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.10%. Comparing base (04857cc) to head (f6ab1ee).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
tools/proto-convert/src/SchemaModifier.ts	95.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #406      +/-   ##
==========================================
+ Coverage   91.86%   95.10%   +3.24%     
==========================================
  Files          15       15              
  Lines        1364     1389      +25     
  Branches      369      382      +13     
==========================================
+ Hits         1253     1321      +68     
+ Misses        110       62      -48     
- Partials        1        6       +5     

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