Rebuild repository as Java backend primitives

[azamir911]

Purpose

Replace the repository contents with a clean-room, independent Java 21 backend primitives library. The implementation does not reuse the previous source files, package names, error identifiers, comments, framework types, or internal terminology.

Complete replacement map

Previous source	Independent replacement
shared/SharedFiFoQueue.java	CloseableBlockingQueue<E> plus the two concrete queue implementations
shared/SharedFiFoLockQueue.java	BoundedBlockingQueue<E> with lock and condition signaling
shared/SharedFiFoSleepingQueue.java	PollingBackoffQueue<E> with configurable backoff
shared/SharedFifoQueueMode.java	QueueWaitStrategy and CloseableQueues factory
queue released exception	QueueClosedException
custom interruption exception	standard InterruptedException with normal interrupt propagation
calculator/Accumulator.java	StreamingStatistics and StatisticsSnapshot
calculator/RatioCalculator.java	DecimalRatioCalculator
calculator/ChunkSizeCalculator.java	AdaptiveBatchSizer, RetryingSizeProbe<T>, and CheckedSizeProbe<T>

Preserved and improved capabilities

Queues

• bounded FIFO ring buffers
• condition-signaling and polling-backoff wait strategies
• blocking and timed producer-consumer operations
• peek, contains, logical indexOf, immutable snapshots, draining, and clearing
• graceful close() with close-and-drain semantics
• atomic closeNow() that discards buffered elements and releases callers
• standard Java interruption behavior

Streaming statistics

• count, sum, mean, sample variance, sample standard deviation, minimum, and maximum
• reset and immutable snapshots
• Welford one-pass variance
• compensated summation
• thread-safe concurrent updates

Decimal ratios

• additive adjustment factor
• explicit scale and RoundingMode
• BigDecimal API and safe double convenience method
• validation for zero denominators and invalid scales

Adaptive batching

• target serialized capacity
• fixed header or protocol overhead
• sample record count and serialized payload measurement
• safety factor and min/max clamps
• retry budget for transient serialization-size failures
• no dependency on a serializer, application type, Spring, Lombok, or company framework

Validation

The final PR head passed:

• Java 21 compilation
• all JUnit 5 unit tests
• multi-producer and multi-consumer stress validation
• concurrent statistics updates
• both queue wait strategies and lifecycle modes
• decimal ratio and rounding edge cases
• adaptive sizing, fallback, clamping, and retry behavior
• Maven verify
• JaCoCo report generation
• JMH executable packaging
• a short JMH run covering both queue wait strategies

Publication plan

The repository remains private during review. After this PR is merged, the previous repository history will be replaced with a clean public history containing only the independent project. The same repository will then be renamed to java-backend-primitives and made public.

No additional repository will be created.