feat: auto-chunk breathing rate and HRV date ranges > 30 days

[veerendra2]

Overview

Fixes #35 by implementing automatic chunking for date ranges > 30 days for Breathing Rate and HRV endpoints using Claude Code CLI (gemini/gemini-3.6-flash model via gateway).

Changes

• fitbit_cli/fitbit_api.py: Added private helper _fetch_chunked_data(self, url_template, key, start_date, end_date=None) to automatically split ranges > 30 days into <= 30-day windows, fetch each chunk, and aggregate response lists (br and hrv).
• fitbit_cli/__init__.py: Bumped version to 1.9.0.
• tests/date_range_test.py: Added unit tests for single date, <= 30 day range, and multi-chunk > 30 day range.

How to Test

1. Unit tests:

   pytest tests/date_range_test.py

2. Local execution with relative dates > 30 days:

   git fetch origin
   git checkout feat/auto-chunk-date-range
   pip3 install -e .
   fitbit-cli -b last-2-months
   fitbit-cli -H last-3-months

[Copilot]

Pull request overview

This PR adds automatic date-range chunking for Breathing Rate and HRV API calls so requests spanning more than 30 days are split into multiple <=30-day requests and then aggregated, preventing Fitbit API errors for long ranges.

Changes:

• Added a private helper in FitbitAPI to fetch and aggregate multi-chunk responses for long date ranges.
• Updated Breathing Rate (summary + intraday) and HRV (summary) endpoints to use the chunking helper.
• Bumped package version and added unit tests covering single-date, <=30-day, and multi-chunk scenarios.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
fitbit_cli/fitbit_api.py	Introduces _fetch_chunked_data() and routes br/hrv endpoints through it to support ranges > 30 days.
fitbit_cli/__init__.py	Version bump to 1.9.0.
tests/date_range_test.py	Adds unit tests validating request chunking behavior and aggregation.

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[veerendra2]

Addressed both Copilot review suggestions:

1. Preserve Top-Level Metadata (fitbit_cli/fitbit_api.py): _fetch_chunked_data now initializes result_dict as a copy of the first chunk's response dictionary before replacing result_dict[key] with the aggregated list. This preserves any top-level metadata fields and keeps behavior consistent with --raw-json output.
2. Strict Call Count Assertion (tests/date_range_test.py): Added self.assertEqual(self.api.make_request.call_count, 2) to test_range_over_30_days_multi_chunk to ensure exact call count enforcement.

All unit tests (35/35) and linters (black, isort, pylint 10/10, mypy) pass cleanly.