Add NIP-13 PoW for geohash with body-only mining animation\n\n- Implement PoW core and defaults (16/15/14 by precision)\n- Wire PoW into geohash send path; hide timestamp while mining\n- Use combined animated text so long messages wrap under name\n- Enforce receive-side PoW filtering for geohash events\n- Filter geohash peer list by observed PoW bits; track per pubkey\n- Stabilize miner memory (autoreleasepool + sched_yield)\n- Add unit tests for PoW

bitchatTests/NostrPoWTests.swift

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+import XCTest
+import CryptoKit
+@testable import bitchat
+
+final class NostrPoWTests: XCTestCase {
+    func testLeadingZeroBits() {
+        // 0x00 -> 8, 0x00 -> 8, 0xF0 -> 0 leading zeros
+        let data = Data([0x00, 0x00, 0xF0]) + Data(repeating: 0x00, count: 29)
+        let lz = NostrPoW.leadingZeroBits(data)
+        XCTAssertEqual(lz, 16)
+    }
+
+    func testMineLowDifficulty() {
+        let pubkey = String(repeating: "a", count: 64)
+        let createdAt = Int(Date().timeIntervalSince1970)
+        let kind = 20000
+        let tags = [["g", "u4pruydqqvj"]]
+        let content = "hello"
+        let targetBits = 8 // keep it very low for test speed
+        let (nonce, idHex) = NostrPoW.mine(pubkey: pubkey, createdAt: createdAt, kind: kind, baseTags: tags, content: content, targetBits: targetBits)
+        XCTAssertGreaterThan(nonce, 0)
+        // Verify difficulty
+        let powTags = tags + [["nonce", String(nonce), String(targetBits)]]
+        // Recompute ID
+        let serialized: [Any] = [0, pubkey, createdAt, kind, powTags, content]
+        let json = try! JSONSerialization.data(withJSONObject: serialized, options: [.withoutEscapingSlashes])
+        let digest = CryptoKit.SHA256.hash(data: json)
+        let idData = Data(digest)
+        XCTAssertEqual(idHex.count, 64)
+        XCTAssertGreaterThanOrEqual(NostrPoW.leadingZeroBits(idData), targetBits)
+    }
+}