Feat: Passthrough fetch, error cause propagation, type refinements, and core improvements

[fern-api]

Changes

• Added makePassthroughRequest - new fetcher utility for raw HTTP passthrough with full unit test coverage
• Added error cause propagation to ManagementError, ManagementTimeoutError, and handleNonStatusCodeError
• Extended Fetcher.ts and makeRequest.ts with passthrough support
• Expanded Client.ts with additional management API methods
• Removed CustomPager.ts to simplify pagination
• Minor type and runtime consistency refinements
• Modernized wire tests across the full suite, reducing boilerplate

[codecov]

Codecov Report

❌ Patch coverage is 87.75510% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.42%. Comparing base (c7ce988) to head (62a2abd).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/management/Client.ts	0.00%	4 Missing ⚠️
src/management/errors/ManagementTimeoutError.ts	0.00%	3 Missing ⚠️
.../management/core/fetcher/makePassthroughRequest.ts	96.87%	2 Missing ⚠️
src/management/core/pagination/Page.ts	0.00%	1 Missing ⚠️
src/management/errors/ManagementError.ts	50.00%	1 Missing ⚠️
src/management/errors/handleNonStatusCodeError.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1318      +/-   ##
==========================================
+ Coverage   89.05%   89.42%   +0.36%     
==========================================
  Files         384      384              
  Lines       18234    18246      +12     
  Branches     8682     9047     +365     
==========================================
+ Hits        16239    16316      +77     
+ Misses       1991     1926      -65     
  Partials        4        4              

Flag	Coverage Δ
alltests	89.42% <87.75%> (+0.36%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/management/api/types/types.ts	100.00% <ø> (ø)
src/management/core/auth/BasicAuth.ts	95.00% <100.00%> (+1.25%)	⬆️
src/management/core/fetcher/BinaryResponse.ts	100.00% <ø> (ø)
src/management/core/fetcher/Fetcher.ts	93.95% <100.00%> (+0.04%)	⬆️
src/management/core/fetcher/index.ts	100.00% <100.00%> (ø)
src/management/core/fetcher/makeRequest.ts	100.00% <100.00%> (ø)
...management/core/form-data-utils/FormDataWrapper.ts	91.30% <100.00%> (ø)
src/management/core/pagination/index.ts	100.00% <ø> (ø)
src/management/core/runtime/runtime.ts	62.50% <100.00%> (-3.22%)	⬇️
src/management/core/pagination/Page.ts	61.53% <0.00%> (ø)
... and 5 more

... and 2 files with indirect coverage changes

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[developerkunal]

LGTM