perf(parser): lazy-load envelopes to reduce Lambda cold start latency by ~900ms

[ErezMizrahi]

Issue number: closes #8406

Summary

Changes

• Replace eager imports of envelopes and BaseEnvelope in parser/__init__.py with a module-level __getattr__ that defers loading until those names are actually accessed
• Add a functional test asserting that importing parse does not load any envelope modules

User experience

Before: Any Lambda function importing parse or event_parser from aws_lambda_powertools.utilities.parser caused all 16 envelope modules to load eagerly at cold start — even when no envelope was ever used.

After: Envelope modules are only imported on first access (e.g. when passing envelope=SqsEnvelope to parse()). Functions that use parse() without an envelope pay zero envelope-loading cost.

Measured impact: ~900ms reduction in Lambda INIT_DURATION for API Gateway handlers using parse() without an envelope. Profiled using PYTHONPROFILEIMPORTTIME=1 on AWS Lambda (arm64, Python 3.13, 1024MB):

# Before
import time:  30627 |   1413849 | aws_lambda_powertools.utilities.parser
import time:   6263 |    295176 |   aws_lambda_powertools.utilities.parser.envelopes
# ... 14 more envelope modules loaded unnecessarily

# After
import time:    312 |     41203 | aws_lambda_powertools.utilities.parser
# No envelope modules loaded

Public API is fully preserved — from aws_lambda_powertools.utilities.parser import envelopes and from aws_lambda_powertools.utilities.parser import BaseEnvelope continue to work exactly as before.

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud