assert.InDeltaSlice: fix lack of length mismatch handling

[puneetdixit200]

Fixes #1263.

InDeltaSlice already compares values by index, but it did not first verify that the two slices had the same length. That meant extra expected values were ignored, while extra actual values could panic by indexing past the expected slice.

This adds an explicit length check before the element-wise comparison. I also added regression coverage for both mismatch directions.

Verification:

• go test ./assert -run TestInDeltaSlice -count=1 failed before the fix: the shorter actual slice passed and the longer actual slice panicked with reflect: slice index out of range
• go test ./assert -run TestInDeltaSlice -count=1
• go test ./assert -count=1
• go test ./... -count=1
• go vet ./...
• gofmt -w assert/assertions.go assert/assertions_test.go
• git diff --check

[puneetdixit200]

Updated in f402eee. InDeltaSlice now follows the InEpsilonSlice validation pattern more closely: it checks the expected value is a slice, uses IsType, uses Len for length mismatches, and reports element failures with the index. Added coverage for mismatched slice types. Verified with go test ./....