feat(#608): human-readable formatting for stats numbers

[tkhhhh]

Summary

Enhancement for #608. The stats tab currently shows raw numeric metrics — nanosecond CPU counters and byte counts — that are hard to read at a glance (e.g. system_cpu_usage: 93579438000000, memory_stats.limit: 2052030464). This PR formats those values into human-readable units before rendering the YAML.

• CPU / nanosecond fields → µs, ms, s, m, h (base 1000)
• Byte fields → KB, MB, GB, TB (base 1024)
• Values below the base unit are left as the raw integer.

Before / After

# before
memory_stats:
  limit: 2052030464
cpu_stats:                                                                                                                                                                               
  system_cpu_usage: 93579438000000
                                                                                                                                                                                         
# after                                                                                                                                                                                
memory_stats:
  limit: 1.911GB
cpu_stats:
  system_cpu_usage: 25.994h

Changes

pkg/utils/utils.go

• FormatBigMetric — formats a big number given a base unit ("bytes" uses 1024, "nanoseconds" uses 1000).
• SetObjectFieldByPath — sets a value at a dotted path inside a nested generic map.

pkg/gui/presentation/container_stats.go

• Introduces PATHS_TO_CONVERT_BIGMETRICS, a whitelist mapping each path of stat with int64 type to its base unit. Covers cpu_stats / precpu_stats (cpu_usage.total_usage, usage_in_kernelmode,
  usage_in_usermode, percpu_usage, system_cpu_usage) and memory_stats (limit, stats.hierarchical_memory_limit, stats.hierarchical_memsw_limit).
• RenderStats now marshals stats to JSON, decodes into a generic map, runs convertBigMetricFromSchema to rewrite the whitelisted fields, and renders the resulting map as YAML.
• convertBigMetric handles both scalar values (float64 from JSON) and per-CPU arrays ([]float64). Missing keys are skipped so containers that don't emit every field still render.

Tests

• pkg/utils/utils_test.go — table tests for FormatBigMetric (unit thresholds, sub-unit values, unknown unit) and SetObjectFieldByPath (nested writes, invalid path).
• pkg/gui/presentation/container_stats_test.go — table tests covering scalar byte/nanosecond conversion, the percpu_usage array path, deeply nested hierarchical_*_limit fields, both cpu_stats and precpu_stats branches, preservation of non-whitelisted fields, and a realistic full-payload snapshot.
• Run lazydocker against a live container, open the stats tab, and confirm whitelisted fields render with units while non-whitelisted numeric fields render unchanged.

Test Result