fix(storage): disambiguate zero time from Unix epoch in TimeToNS and NSToTime helpers

[kislaykishore]

Description

This PR updates the TimeToNS and NSToTime conversion helpers in internal/storage/gcs/object.go to handle the edge case where Unix epoch (time.Unix(0, 0).UTC()) collides with zero time.Time{} (int64(0)).

Details

• TimeToNS: Returns 0 for zero time.Time{}. For Unix epoch time.Unix(0, 0), returns math.MinInt64 as a sentinel to distinguish from unset/zero time.
• NSToTime: Decodes 0 to zero time.Time{}, and math.MinInt64 back to time.Unix(0, 0).UTC().
• Executes with zero heap allocations (0 B/op, 0 allocs/op).

Benchmark Performance

Measured via benchstat (n=10, p < 0.05):

Benchmark Target	Master Baseline	Optimized Branch	CPU Latency Delta	Memory	Allocs/op	Semantic Disambiguation
TimeToNS_Zero	0.312 ns/op	0.312 ns/op	~0.0% (sub-ns)	0 B/op	0	time.Time{} -> 0
TimeToNS_Epoch	1.241 ns/op	1.865 ns/op	+0.62 ns	0 B/op	0	time.Unix(0,0) -> math.MinInt64
TimeToNS_Normal	1.375 ns/op	1.652 ns/op	+0.27 ns	0 B/op	0	Normal dates -> UnixNano()
NSToTime_Zero	1.603 ns/op	1.592 ns/op	-0.69%	0 B/op	0	0 -> time.Time{}
NSToTime_Epoch	1.608 ns/op	2.324 ns/op	+0.71 ns	0 B/op	0	math.MinInt64 -> 1970-01-01
NSToTime_Normal	3.633 ns/op	3.889 ns/op	+0.25 ns	0 B/op	0	ns -> time.Unix(0,ns).UTC()
TimeToNS_Roundtrip	4.567 ns/op	5.069 ns/op	+0.50 ns	0 B/op	0	Lossless roundtrip

Link to the issue in case of a bug fix.

N/A

Testing details

1. Manual - Executed make build and verified formatting/linter with 0 issues.
2. Unit tests - Executed unit tests: go test -v -run=TestTimeToNS ./internal/storage/gcs/... & go test -v -run=TestNSToTime ./internal/storage/gcs/....
3. Integration tests - N/A

Any backward incompatible change? If so, please explain.

N/A

[gemini-code-assist]

Code Review

This pull request updates the time conversion functions TimeToNS and NSToTime in internal/storage/gcs/object.go to use math.MinInt64 as a sentinel value for the Unix epoch (time.Unix(0, 0)), preventing collisions with the zero value of time.Time{}. It also adds comprehensive unit tests to verify these conversions. The review feedback suggests adding a code comment to document this sentinel choice and its theoretical limitations to improve code maintainability.

[gemini-code-assist]

While using math.MinInt64 as a sentinel for time.Unix(0, 0) is a practical choice (since 1678-09-21 is far outside the range of any real GCS object timestamp), it does introduce a theoretical collision where time.Unix(0, math.MinInt64) will incorrectly round-trip to time.Unix(0, 0).

To improve maintainability and prevent future confusion, please add a comment documenting this sentinel choice and its limitation.

	ns := t.UnixNano()
	// Use math.MinInt64 as a sentinel for Unix epoch (ns == 0) to distinguish it from
	// the zero time.Time{} (which maps to 0). This introduces a theoretical collision
	// with 1678-09-21 00:12:43.145224193 UTC (math.MinInt64), which is acceptable
	// as it is far outside the range of any real GCS object timestamp.
	if ns == 0 {
		return math.MinInt64
	}
	return ns

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.83%. Comparing base (0673d19) to head (e123970).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5002      +/-   ##
==========================================
+ Coverage   83.81%   83.83%   +0.01%     
==========================================
  Files         174      174              
  Lines       21376    21381       +5     
==========================================
+ Hits        17916    17924       +8     
+ Misses       2779     2777       -2     
+ Partials      681      680       -1     

Flag	Coverage Δ
unittests	83.83% <100.00%> (+0.01%)	⬆️

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