ci(ios): make SPV workflow test opt-in

[hechibing]

• Skip RestNodeApiTests.testSPVWorkflow on CI unless ERGO_SPV_WORKFLOW_TEST=1

• Allow overriding nodes via ERGO_SPV_PROOF_NODE_1/2 and ERGO_SPV_VERIFY_NODE

• Fix SwiftyJSON Optional handling for Swift 6 (remove unreachable case nil)

[coveralls]

Pull Request Test Coverage Report for Build 22026708837

Details

• 13 of 18 (72.22%) changed or added relevant lines in 1 file are covered.
• 290 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.9%) to 85.997%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
ergo-rest/src/api/node.rs	13	18	72.22%

Files with Coverage Reduction	New Missed Lines	%
ergotree-ir/src/chain/token.rs	9	74.29%
ergo-chain-types/src/peer_addr.rs	10	68.0%
ergo-rest/src/api/node.rs	126	10.27%
ergo-rest/src/api/peer_discovery_internals/non_chrome.rs	145	8.02%

Totals
Change from base Build 21705206395:	-0.9%
Covered Lines:	27201
Relevant Lines:	31630

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💛 - Coveralls