Add non-blocking locator stability signals: core models, Selenium sampler, evaluator, and tests

[ajayrakde]

Motivation

• Implement Priority Add sync kernel readiness framework with Selenium implementation and default policies #5 stability signals to provide non-blocking sampling and pure evaluators (snapshots only) for element/container/global UI stability without adding any waiting logic.
• Keep the stability layer free of sleeps/blocking so higher-level kernels (Add actionability pipeline for Locator actions #2/Add non-blocking locator stability signals: core models, Selenium sampler, evaluator, and tests #3) can decide sampling windows and waits.
• Provide a Selenium adapter that performs a single JS round-trip per sample and returns a compact payload suitable for diagnostics and evaluation.

Description

• Add core signal models and config records under org.openqa.selenium.locator.stability.model including Rect, VisibilityFlags, StabilitySnapshot, GlobalStabilitySnapshot, StabilityHistory, and StabilityConfig with defaultConfig().
• Add core APIs under org.openqa.selenium.locator.stability.api including Clock, SystemClock, StabilitySampler, StabilityEvaluator, and StabilityService.
• Implement Selenium integration under org.openqa.selenium.locator.stability.selenium and ...selenium.impl with SeleniumStabilityService, JsStabilitySampler, DefaultStabilityService, and DefaultStabilityEvaluator, plus JS payloads and parsing in JsScripts and JsResultParser.
• Add documentation java/docs/locator-stability-signals.md and update the locator user-journey doc to note the non-blocking stability sampling behavior, and wire unit tests into the Bazel test suite (java/test/... changes).
• Add unit tests for the parser, evaluator, service append logic, and an architecture guardrail test (StabilityArchitectureTest) that asserts stability package bytecode does not reference Thread.sleep, WebDriverWait, or ExpectedConditions.

Testing

• Added unit tests: JsResultParserTest, DefaultStabilityEvaluatorTest, DefaultStabilityServiceTest, and StabilityArchitectureTest (all tagged as unit tests).
• Attempted to run bazel test //java/test/org/openqa/selenium:SmallTests, but the run failed in this environment because Bazel could not be downloaded from releases.bazel.build (HTTP/permission error), so tests could not be executed here.
• The new architecture test is designed to run in CI to enforce the no-waits/no-sleeps guardrail and the other unit tests validate parsing, evaluator correctness, and bounded-history behavior when executed in a full build environment.

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Codex Task