otlp: Respect backoff in retry time limit

[Sakshamm-Goyal]

Fixes #8781.

The retry loop already waits for the greater of the exponential backoff and server throttle, but its remaining-budget check only included the throttle. When backoff was greater, an exporter could wait past MaxElapsedTime and issue another request.

This changes the budget check to use the selected delay and adds the regression to the shared retry template, regenerating all six OTLP trace, metric, and log HTTP/gRPC implementations.

Validation:

• reproduced the regression before the fix in the generated trace HTTP retry package
• exact regression passes in all six generated retry packages
• full retry suites pass in all six generated packages
• make precommit passes, including generation, tidy, lint, README/module verification, and repository-wide race tests
• git diff --check passes

[linux-foundation-easycla]

• ❌ - login: @Sakshamm-Goyal / name: Saksham Goyal. The commit (6d3585b, acb1e14) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please visit our EasyCLA portal and chat with our support bot.

[MrAlias]

@Sakshamm-Goyal please sign the CLA so these changes can be considered.