fix: mirror node contract query

[radkomih]

Description:

Fix flaky mirror-node contract-query e2e tests that intermittently failed with an EOF transport error when the local JSON-RPC relay dropped connections under load. performContractCallToMirrorNode used a bare http.Post with no timeout or retry, so a transient connection drop surfaced as an unhandled transport error instead of being retried or returning the intended HTTP result.

Add a shared mirror-node POST helper with bounded retries, backoff, and an explicit timeout, and route the contract query and fee-estimate query through it.

• Add mirrorNodePostWithRetry and mirrorNodeShouldRetry in sdk/mirror_node_rest_helpers.go — retries transport errors and 5xx/429 with exponential backoff (capped at 8s, default 3 attempts), uses an http.Client with an explicit timeout (30s default), and does not retry genuine 4xx responses
• Route performContractCallToMirrorNode through the helper and return a clear error on a nil response
• Refactor FeeEstimateQuery.callGetFeeEstimate to reuse the helper and remove its duplicated inline retry loop
• Remove the now-unused FeeEstimateQuery.shouldRetry wrapper and repoint its unit test at mirrorNodeShouldRetry
• Add unit tests covering transient 5xx retry, transport-error (EOF) retry, and no-retry on 4xx

Related issue(s):

Fixes #1752
Fixes #1753

Notes for reviewer:

Both issues share the same root cause (the bare http.Post in performContractCallToMirrorNode), so this single change closes both. 4xx responses are intentionally not retried, preserving the "received non-200 response from Mirror Node" assertion in TestMirrorNodeContractQueryFailWhenGasLimitIsLow (#1752), while transient EOF/5xx are now retried, fixing the TestUint8*/TestUint16* success-path flakiness (#1753).

Checklist

• Unit tests
• Integration tests

[lfdt-bot]

✅ Snyk checks have passed. No issues have been found so far.

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[radkomih]

need to perform the e2e tests

[codecov]

Codecov Report

❌ Patch coverage is 84.44444% with 7 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
sdk/mirror_node_rest_helpers.go	90.62%	2 Missing and 1 partial ⚠️
sdk/fee_estimate_query.go	80.00%	2 Missing ⚠️
sdk/mirror_node_contract_query.go	33.33%	1 Missing and 1 partial ⚠️

Files with missing lines	Coverage Δ
sdk/fee_estimate_query.go	78.44% <80.00%> (-0.72%)	⬇️
sdk/mirror_node_contract_query.go	66.92% <33.33%> (-1.08%)	⬇️
sdk/mirror_node_rest_helpers.go	90.62% <90.62%> (ø)

... and 2 files with indirect coverage changes

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[Dosik13]

can you add more test coverage?