Bump all dependencies to latest stable versions

[Copilot]

Project dependencies were significantly outdated (Kotlin 1.7, Ktor 2.1, Gradle 6.8). This updates the full dependency graph to current stable releases and fixes resulting API compatibility issues.

Dependency upgrades

Dependency	From	To
Gradle wrapper	6.8	8.10
Kotlin	1.7.10	2.1.21
Ktor	2.1.0	3.1.3
kotlinx-serialization-json	1.4.0	1.8.1
kotlinx-coroutines-core	1.6.4	1.10.2
kotest	4.6.2 / 5.4.2	5.9.1 (unified)
logback-classic	1.2.10	1.5.18

API compatibility fixes

• Ktor 3.x: Removed ktor-client-serialization-jvm from browserstack module — this artifact was dropped in Ktor 3.x; content negotiation was already handled via ktor-client-content-negotiation in core.
• kotest 5.x: Replaced deprecated testCase.displayName with testCase.name.testName throughout examples/common.
• kotest version skew: core module was pinned to 4.6.2 while all other modules used 5.4.2 — now uniformly 5.9.1.

Original prompt

проанализируй готовность проекта, обновить зависимости.

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