Min time becomes measurement option

[oleksandr-pavlyk]

--min-time is now a part of nvbench::benchmark_base, nvbench::state.

min-time used to be stdrel-stopping-criterion parameter, but
was being used by hot measuring loop (see #408).

This PR add m_min_time data member to benchmark_base and state
classes as measurement option, same as --min-samples. Setter/getter
methods are added.

Option parser is modified to recognize --min-time <duration> as option associated
with benchmark and calls .set_min_time(duration) setter.

Measuring loops have access to min-time parameter, but delegate
what to do with measurement options (--min-time and --min-samples)
to individual stopping criteria via new stopping criteria method
bool is_elibigible_to_stop(stopping_context context).

The stopping_context argument contains the number-of-samples collected,
min-samples, total-sample-time, min-time. The method allows stopping
criteria to customize treatment of measurement options:

• stdrel: honors both --min-time and --min-samples (same as before)
• entropy: honors --min-samples, ignores --min-time (same as before)
• target-samples: ignores both (intentional change)

Closes #408.

CLI option --min-time is now always recognized, irrespective of which
stopping-criterion is current during option parsing.

Python API modified to match C++.

docs/cli_help.md modified:

• --min-time moved to measurement options section
• each documented stopping criterion states how it takes measurement options into account

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📥 Commits

Reviewing files that changed from the base of the PR and between 5061a4f and 0e4748d.

📒 Files selected for processing (34)

• docs/cli_help.md
• examples/CMakeLists.txt
• nvbench/benchmark_base.cuh
• nvbench/benchmark_base.cxx
• nvbench/detail/measure_cold.cu
• nvbench/detail/measure_cold.cuh
• nvbench/detail/measure_cpu_only.cuh
• nvbench/detail/measure_cpu_only.cxx
• nvbench/detail/measure_hot.cu
• nvbench/detail/measure_hot.cuh
• nvbench/detail/measure_timeout_warnings.cuh
• nvbench/detail/sample_count_criterion.cuh
• nvbench/detail/sample_count_criterion.cxx
• nvbench/detail/stdrel_criterion.cuh
• nvbench/detail/stdrel_criterion.cxx
• nvbench/detail/validate_min_time.cuh
• nvbench/json_printer.cu
• nvbench/option_parser.cu
• nvbench/state.cuh
• nvbench/state.cxx
• nvbench/stopping_criterion.cuh
• python/cuda/bench/__init__.pyi
• python/cuda/bench/_decorators.py
• python/src/py_nvbench.cpp
• python/test/test_cuda_bench.py
• testing/benchmark.cu
• testing/entropy_criterion.cu
• testing/exception_safety.cu
• testing/measure_timeout_warnings.cu
• testing/option_parser.cu
• testing/sample_count_criterion.cu
• testing/state.cu
• testing/state_generator.cu
• testing/stdrel_criterion.cu

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📝 Walkthrough

Summary by CodeRabbit

• New Features
  • Added minimum accumulated measurement time controls (--min-time, plus C++/Python min_time/set_min_time APIs) and included min_time in JSON output.
  • Stopping criteria now use a shared stopping context to coordinate minimum samples and minimum time.
• Documentation
  • Refreshed CLI help to clarify --min-time interaction with --stopping-criterion.
• Bug Fixes
  • Updated timeout-warning logic and stopping eligibility so warnings reflect true minimum-time blocking.
• Tests
  • Expanded coverage for option parsing/validation, stopping-context behavior, decorator/API wiring, and JSON emission.

Walkthrough

The change models --min-time as benchmark measurement configuration, propagates it through benchmark state and stopping contexts, updates criterion eligibility and timeout warnings, exposes Python APIs, updates documentation and examples, and adds coverage for parsing and stopping behavior.

Changes

Minimum measurement time

Layer / File(s)	Summary
Configuration and stopping contract nvbench/benchmark_base.*, nvbench/state.*, nvbench/stopping_criterion.cuh, nvbench/option_parser.cu, nvbench/json_printer.cu	Minimum-time configuration is validated, stored on benchmarks and states, parsed from --min-time, copied through generated state, included in stopping contexts, and emitted in JSON results.
Criterion and measurement execution nvbench/detail/measure_*, nvbench/detail/*criterion.*, nvbench/detail/measure_timeout_warnings.cuh	Cold and CPU-only measurements pass sample/time context to stopping criteria; hot measurements use a separate batch target time; stdrel and sample-count define eligibility behavior; timeout warnings use criterion-aware minimum-time checks.
Public interfaces and usage python/cuda/bench/*, python/src/py_nvbench.cpp, docs/cli_help.md, examples/CMakeLists.txt	Python benchmark/state APIs and decorators expose minimum-time configuration, CLI help describes shared semantics, and all examples receive the option.
Behavioral validation testing/*, python/test/test_cuda_bench.py	Tests cover validation, criterion context rules, CLI parsing and propagation, timeout warnings, state generation, exception safety, Python decorators, and updated stdrel behavior.

Assessment against linked issues

Objective	Addressed	Explanation
Move --min-time out of stdrel criterion parameters and make it usable with other criteria [#408]	✅

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[oleksandr-pavlyk]

This work is superseded by #439.

The important drawback here is that while making --min-time a global option makes it possible to set it regardless of the stopping-criterion selected, this knob controls both measure_hot and stdrel criterion used by measure_cold at the same time. Those controls need to be separate as explained in #442

This pull request should be closed without merging once #439 lands.