Batch-settlement: go-ts parity

[phdargen]

Description

commit 4cfb896:

• After a full cooperative refund, the server-side channel file should be deleted, and after a successful paid request the pendingRequest should be cleared
• Request context identity breaks when payload is enriched => implemented deterministic key built only from immutable request fields
• Added missing pendingRequest cleanup on failures: OnVerifyFailureHook() and OnSettleFailureHook() clean up

commit 691decb:

• fixed lint

commit 40facfa:

• removed duplicate payer info from storage

commit e300927:

• fixed PAYMENT-RESPONSE field ordering

commit 64d20cf:

• cleaned up comments removing TS implementation references

commit 9417394:

• consolidated ProcessSettlementWithExtensions into ProcessSettlement

Checklist

• I have formatted and linted my code
• All new and existing tests pass
• My commits are signed (required for merge) -- you may need to rebase if you initially pushed unsigned commits
• I added a changelog fragment for user-facing changes (docs-only changes can skip)

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