test: add unit tests for LoggingInterceptor, HttpExceptionFilter, Sta…

[yahia008]

Title:

test: add unit tests for LoggingInterceptor, HttpExceptionFilter, and StatsService

Description:

Summary

Adds missing unit test coverage for three untested modules across the codebase.

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LoggingInterceptor (src/common/logging.interceptor.spec.ts)

• Verifies the log message format is METHOD URL STATUS Nms
• Asserts the response stream passes through unchanged
• Confirms no log is emitted when the handler errors (error propagates to subscriber)
• Checks statusCode is read inside the tap callback, not captured at intercept time
• Covers multi-value observable streams and non-negative duration values

HttpExceptionFilter (src/common/http-exception.filter.spec.ts)

Tests all four distinct response-shape branches explicitly:

• Branch 1 — string body → { error: string }
• Branch 2 — validation-array body (message: string[]) → { error: "Validation failed", details: [...] }
• Branch 3 — custom-shaped body with error string passes through as-is
• Branch 4 — object body with a string message → { error: message }
• Branch 5 — non-HttpException errors → 500, logger.error called; non-Error throws and null handled gracefully

StatsService (src/stats/stats.service.spec.ts)

Covers all aggregation edge cases:

• Empty store all-zero guard
• totalVolume BigInt reduce with missing fillAmount, large precision values beyond Number.MAX_SAFE_INTEGER, result always returned as a string
• avgFillTime with no filled intents, all filledAt unset, correct rounding, and exclusion of intents missing filledAt
• fillRate divide-by-zero guard (intents.length === 0 → 0)
• uniqueUsers deduplication via Set
• activeSolvers filtering by isActive: true

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Closes #101
Closes #102
Closes #103

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