Fix OTEL metric names and parameter types

[satyakigh]

What changed

1. OTEL metric name sanitization (ScopedTelemetry.ts) — Added a sanitizeMetricName() function that lowercases metric names and replaces invalid characters with underscores
   to comply with the OpenTelemetry naming spec (/^[a-z][a-z0-9_.-/]{0,254}$/i). This sanitization is now applied in all four metric creation paths: counters, up-down
   counters, histograms, and observable gauges.

2. Parameter type coercion hardening (ParameterType.ts) — Two fixes:

   • isNumericType() was using .includes('Number') which could false-positive on types like AWS::SSM::Parameter::Value<List>. Now it strictly checks
     === ParameterType.Number.
   • coerceParameterToTypedValues() now validates the types of Default and AllowedValues before using them (guards against unexpected types sneaking through), and fixes the
     boolean detection logic so AllowedValues takes precedence over Default when both are present.

3. Constructor visibility (ScopedTelemetry.ts / TelemetryService.ts) — Made the ScopedTelemetry constructor private so only TelemetryService (the intended owner) can
   instantiate it. TelemetryService and tests use @ts-expect-error to bypass this.

Why / What it fixes

• Metric names with characters outside the OTEL spec (e.g., spaces, special chars) would silently create invalid metrics or get rejected by OTEL exporters. The sanitizer
  prevents that.
• The loose isNumericType check and unguarded type coercion could misclassify parameter types, leading to incorrect completions or validation behavior for CloudFormation
  template parameters.
• Making the constructor private enforces the design intent that ScopedTelemetry instances should only be created through TelemetryService.