Use environment variables for S3 bucket prefixes

[nickclyde]

Description

This PR standardizes the use of environment variables for S3 bucket and key prefixes, refactors S3 client usage for efficiency and testability, and updates tests and helper functions accordingly.

Lambda Handler (packages/lambda-handler/src/lambda_handler/lambda_handler.py):

• Added optional s3_client parameter to get_file_content_from_s3() and put_file() for client reuse

TTC Lambda (packages/text-to-code-lambda/src/text_to_code_lambda/lambda_function.py):

• Added S3_BUCKET env var (default: dibbs-text-to-code)
• Updated TTC_INPUT_PREFIX default to TextToCodeValidateSubmissionV2/
• Removed all .split("/")[0] bucket derivations. Now uses S3_BUCKET + prefix as object key
• Threaded s3_client through helper functions

Augmentation Lambda (packages/augmentation-lambda/src/augmentation_lambda/lambda_function.py):

• Added S3_BUCKET, AUGMENTED_EICR_PREFIX, AUGMENTATION_METADATA_PREFIX env vars
• Added S3 client caching and S3 writes for augmented eICR and metadata after augmentation

Augmentation main.py (packages/augmentation/src/augmentation/main.py):

• Replaced hardcoded bucket names with env var driven pattern

Terraform:

• _variables.tf: Updated ttc_input_prefix default, added augmented_eicr_prefix and augmentation_metadata_prefix variables
• main.tf: Renamed BUCKET_NAME → S3_BUCKET

Tests: Updated all test fixtures and assertions for the single-bucket + prefix pattern. All 27 tests pass across all three packages.

Related Issues

Closes #349

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.96970% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 93.73%. Comparing base (13c0bb0) to head (a8dae11).

Files with missing lines	Patch %	Lines
...-lambda/src/augmentation_lambda/lambda_function.py	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #395      +/-   ##
==========================================
- Coverage   93.75%   93.73%   -0.02%     
==========================================
  Files          42       42              
  Lines        2145     2156      +11     
==========================================
+ Hits         2011     2021      +10     
- Misses        134      135       +1     

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[robertandremitchell]

lgtm!

[BradySkylight]

Nice work... some clean-up along the way with some good naming conventions and using env variables. 🚀