feat(token): integrate indexer provider

[dhyaniarun1993]

Closes #192

[gemini-code-assist]

Code Review

This pull request introduces an alternative "indexer" mode for the token data provider, allowing the system to query balances and total supply via a pre-materialized HTTP API instead of live gRPC scans. Key changes include the implementation of an HTTP client for the indexer, a new indexer-backed provider, and configuration updates to support mode selection. Feedback was provided to improve the robustness of error handling in the indexer client by ensuring that raw response bodies are captured as a fallback when JSON error decoding fails for non-2xx status codes.

[salindne]

Small fix, otherwise looks great

[codecov-commenter]

Codecov Report

❌ Patch coverage is 17.07317% with 34 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@54b8844). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
pkg/app/api/server.go	0.00%	30 Missing ⚠️
pkg/config/config.go	66.66%	1 Missing and 1 partial ⚠️
pkg/indexer/client/http.go	60.00%	1 Missing and 1 partial ⚠️

❌ Your patch status has failed because the patch coverage (17.07%) is below the target coverage (50.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #195   +/-   ##
=======================================
  Coverage        ?   32.92%           
=======================================
  Files           ?      123           
  Lines           ?     8563           
  Branches        ?        0           
=======================================
  Hits            ?     2819           
  Misses          ?     5494           
  Partials        ?      250           

Flag	Coverage Δ
unittests	32.92% <17.07%> (?)

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Files with missing lines	Coverage Δ
pkg/config/config.go	71.18% <66.66%> (ø)
pkg/indexer/client/http.go	86.66% <60.00%> (ø)
pkg/app/api/server.go	0.00% <0.00%> (ø)

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