Added RateLimitedSampler

[rads-1996]

Description

Adding support for RateLimitedSampler, inspired by Java Application Insights sampler
https://github.com/microsoft/ApplicationInsights-Java/blob/main/agent/agent-tooling/src/main/java/com/microsoft/applicationinsights/agent/internal/sampling/RateLimitedSamplingPercentage.java

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[Copilot]

Pull Request Overview

This PR adds support for a rate-limited sampler alongside the existing fixed-percentage sampler in the Azure Monitor OpenTelemetry SDK. Key changes include:

• Introducing new constants and environment variable handling for RATE_LIMITED_SAMPLER and sampling traces per second.
• Updating _get_configurations, _configure, and SDK constants to select between rate-limited and fixed-percentage samplers.
• Implementing RateLimitedSampler, utility functions (_get_djb2_sample_score, _round_down_to_nearest), and comprehensive tests for sampling behavior.

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/utils/test_configurations.py	Added tests for rate-limited and fixed-percentage sampler env var scenarios
_constants.py (SDK)	Defined RATE_LIMITED_SAMPLER, FIXED_PERCENTAGE_SAMPLER, and SAMPLING_TRACES_PER_SECOND_ARG
configurations.py	Enhanced _default_sampling_ratio to branch on sampler type and set appropriate configuration
_configure.py	Updated setup to instantiate RateLimitedSampler when traces-per-second is set
exporter/_utils.py	Added _get_djb2_sample_score and improved rounding logic
_rate_limited_sampling.py	Implemented RateLimitedSamplingPercentage and RateLimitedSampler
exporter/_constants.py	Defined hash and integer bounds for sampling utilities

[rads-1996]

The existing sampler - ApplicationInsightsSampler, has a lot of constants, methods defined internally in _sampling.py that I have defined in constants.py and utils. If needed I can create another PR for that sampler, so it also references the methods and variables just like the new one does.

[rads-1996]

A fresh one created