feat(NODE-7467): make token bucket optional in client backpressure

[tadjik1]

Description

Summary of Changes

Node.js implementation of recent addition into client backpressure spec (token bucket is optional and disabled by default).
Spec PR: mongodb/specifications#1902

Notes for Reviewers

What is the motivation for this change?

Release Highlight

Release notes highlight

Double check the following

• Lint is passing (npm run check:lint)
• Self-review completed using the steps outlined here
• PR title follows the correct format: type(NODE-xxxx)[!]: description
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[nbbeeken]

@tadjik1 With the specific spec PR and the whole of backpressure now on main in the specifications repo is this ready? :)

[Copilot]

Pull request overview

Adds support for the client backpressure spec update where the token bucket mechanism is optional (disabled by default) and controlled via a new adaptiveRetries option.

Changes:

• Introduces adaptiveRetries as a parsed URI/client option with a default of false.
• Gates token-bucket deposit/consume behavior during overload retries behind adaptiveRetries.
• Adds unit/integration/spec tests covering option parsing and retry behavior (including max retry count and token bucket limiting).

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/connection_string.ts	Adds adaptiveRetries to connection string option descriptors with default false.
src/mongo_client.ts	Exposes adaptiveRetries on MongoClientOptions and makes it required on parsed MongoOptions.
src/sdam/topology.ts	Plumbs adaptiveRetries into TopologyOptions for downstream retry behavior checks.
src/operations/execute_operation.ts	Makes token bucket accounting/enforcement conditional on adaptiveRetries.
test/unit/connection_string.test.ts	Verifies adaptiveRetries default and enabling via URI/options.
test/tools/uri_spec_runner.ts	Adds adaptiveRetries to the URI spec runner’s directly-mapped option assertions.
test/spec/uri-options/client-backpressure-options.yml	New URI option spec cases for adaptiveRetries parsing and invalid values.
test/spec/uri-options/client-backpressure-options.json	JSON equivalent of the new adaptiveRetries URI spec cases.
test/integration/client-backpressure/client-backpressure.prose.test.ts	Updates/adds prose tests for token bucket enforcement and overload retry limits.

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