fix(metrics): send timestamps as Unix seconds instead of milliseconds to API

[platinummonkey]

Summary

Fixed a bug where the metrics query command was sending timestamps in milliseconds instead of seconds to the Datadog v2 timeseries API, causing queries to fail or return incorrect time ranges.

Problem

The parseTimeParam function correctly parses user input (e.g., --from="1h", --from="1704067200") as Unix seconds, but the code was then converting these to milliseconds via .UnixMilli() before sending to the API. The Datadog v2 timeseries API expects timestamps in seconds, not milliseconds.

Changes

• Changed from.UnixMilli() to from.Unix() in runMetricsQuery (cmd/metrics.go:510)
• Changed to.UnixMilli() to to.Unix() in runMetricsQuery (cmd/metrics.go:511)
• Updated documentation to clarify timestamps are in seconds (cmd/metrics.go:126-127)

Testing

• All existing tests pass
• Verified no other code uses the incorrect .UnixMilli() pattern for API calls

Impact

Users can now correctly query metrics with time ranges like:

pup metrics query --query="avg:system.cpu.user{*}" --from="1h" --to="now"
pup metrics query --query="avg:system.cpu.user{*}" --from="1704067200" --to="1704153600"

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🤖 Generated with Claude Code

[github-actions]

📊 Test Coverage Report

Overall Coverage: 75.1%

Threshold: 80% ❌

Coverage by Package

## Coverage by Package

- github.com/DataDog/pup/pkg/auth/callback/server.go:40: 81.2%
- github.com/DataDog/pup/pkg/auth/dcr/client.go:28: 100.0%
- github.com/DataDog/pup/pkg/auth/dcr/types.go:24: 100.0%
- github.com/DataDog/pup/pkg/auth/oauth/client.go:22: 100.0%
- github.com/DataDog/pup/pkg/auth/oauth/pkce.go:24: 85.7%
- github.com/DataDog/pup/pkg/auth/storage/factory.go:53: 94.7%
- github.com/DataDog/pup/pkg/auth/storage/keychain.go:44: 42.9%
- github.com/DataDog/pup/pkg/auth/storage/storage.go:58: 71.4%
- github.com/DataDog/pup/pkg/auth/types/types.go:23: 100.0%
- github.com/DataDog/pup/pkg/client/client.go:28: 94.1%
- github.com/DataDog/pup/pkg/config/config.go:22: 100.0%
- github.com/DataDog/pup/pkg/formatter/formatter.go:31: 100.0%
- github.com/DataDog/pup/pkg/util/time.go:20: 95.8%

## Summary

total:								(statements)		75.1%

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📈 Coverage Status: ❌ FAILED - Coverage below minimum threshold

_{Updated for commit 5022dcc}