feat: expose the Sentry settings that cost RPS

[lesnik512]

Closes #186.

Three Sentry settings that measurably cost RPS were reachable only by hand-building
sentry_integrations or stuffing sentry_additional_params. All three are now config fields.

What changed

• sentry_logs_level=None by default. Unless sentry_integrations already contains a
  LoggingIntegration, SentryInstrument appends
  LoggingIntegration(level=sentry_logging_breadcrumb_level, sentry_logs_level=None).
• sentry_auto_session_tracking: bool = True, passed to sentry_sdk.init. Default unchanged.
• sentry_logging_breadcrumb_level: int | None = logging.INFO, the breadcrumb handler's level.
  Default unchanged; None disables breadcrumbs.

Why the appended integration is behaviour-preserving

sentry_sdk.integrations.setup_integrations builds {integration.identifier: integration} and only
fills a default in if integration_cls.identifier not in integrations, so a user-supplied
LoggingIntegration still wins. The appended one differs from sentry-sdk's own default integration
in exactly one handler: EventHandler(ERROR) and BreadcrumbHandler(INFO) are untouched, only
SentryLogsHandler goes away.

That handler is pure waste here. lite-bootstrap never sets enable_logs, so Sentry Logs is off, but
SentryLogsHandler.emit calls self.format(record) before it checks
has_logs_enabled(client.options) — filed upstream as
getsentry/sentry-python#7402. Even if that
lands, sentry_logs_level=None remains the correct configuration while the feature is unsupported.

When sentry_default_integrations=False the integration is not appended. Appending it would add
an integration the user explicitly disabled, so the opt-out has to win.

sentry_additional_params now overrides instead of colliding

Adding auto_session_tracking as an explicit init kwarg broke every user who had reached it the
documented way — the issue itself describes these settings as reachable "by stuffing
sentry_additional_params":

TypeError: sentry_sdk._init_implementation._init() got multiple values for keyword argument 'auto_session_tracking'

bootstrap() now builds an init_params dict that sentry_additional_params updates, so it
overrides the explicit kwargs for every field rather than colliding with them. Nothing that works
today changes behaviour: a key collision was already a TypeError.

An ignored knob warns

sentry_logging_breadcrumb_level cannot apply when the user supplies their own LoggingIntegration
or sets sentry_default_integrations=False. Rather than fail silently, it goes through
warn_at_caller, naming which of the two reasons applies — the same shape as
"swagger_path differs from docs_url, ... will be used" in fastapi_bootstrapper.py. The warning
only fires when the field is off its default, so a user who never touched it never sees it.

Docs and benchmarks

docs/introduction/configuration.md documents the three fields, the appended integration and both
opt-outs, linking benchmarks/README.md §4c for the numbers rather than copying the table.

benchmarks/README.md asserted the opposite of the code in several places, some of it stale since
before this branch:

• §4a was titled "two knobs lite-bootstrap does not expose" and said "There is no configuration
  surface for a sampler anywhere in lite-bootstrap". Both OpenTelemetry sampler is not configurable #184 and Pass exclude_spans to FastAPIInstrumentor so ASGI send/receive spans are opt-out #185 have since shipped as
  opentelemetry_sampler and opentelemetry_exclude_spans.
• §6's tuned configuration hand-built LoggingIntegration(level=None, sentry_logs_level=None) and
  sentry_additional_params={"auto_session_tracking": False}, and carried the OTel knobs as a
  comment reading "not expressible today". It now uses the real fields throughout. I ran the new
  spelling and confirmed it produces an identical client: _breadcrumb_handler None,
  _sentry_logs_handler None, _handler EventHandler(ERROR), auto_session_tracking False.
• §7 was headed "nothing implemented" while listing three issues that are now implemented.

Not done, deliberately

• No sentry_logs_level config field, despite the symmetry with the breadcrumb knob. Any
  non-None value is pure waste while lite-bootstrap does not support Sentry Logs, so the knob would
  be generality with no need behind it.
• No ADR. The decision is a one-line reversal and its rationale lives in the configuration docs,
  so it fails the "hard to reverse" test.

Testing

Nine new tests in tests/instruments/test_sentry_instrument.py covering the disabled logs handler,
a user-supplied integration winning, sentry_default_integrations=False, both knobs reaching the
client, sentry_additional_params overriding, and the warning firing and staying quiet.

307 tests pass; ruff format, ruff check, ty and a strict mkdocs build are clean.