Validate monitoring_location_id format in waterdata functions

[thodson-usgs]

Summary

Closes #188.

Passing an integer or a bare string (without the required AGENCY-ID prefix) to a waterdata function silently wasted an API call and returned confusing empty results. Now all 10 public functions that accept monitoring_location_id raise immediately before any network call:

# Before: silent empty result
get_daily(monitoring_location_id=5129115, parameter_code="00060")
get_daily(monitoring_location_id="dog", parameter_code="00060")

# After:
# TypeError: monitoring_location_id must be a string or list of strings, not int.
#            Expected format: 'AGENCY-ID', e.g., 'USGS-5129115'.
# ValueError: Invalid monitoring_location_id: 'dog'.
#             Expected 'AGENCY-ID' format, e.g., 'USGS-01646500'.

Functions covered: get_daily, get_continuous, get_monitoring_locations, get_time_series_metadata, get_latest_continuous, get_latest_daily, get_field_measurements, get_stats_por, get_stats_date_range, get_channel

Validation rules:

• Must be a str or list[str] (not int, float, etc.) → TypeError
• Each string must contain a - separator (AGENCY-ID format) → ValueError
• None is allowed (optional parameter)

Test plan

• 9 unit tests covering: valid inputs, None, bare integer, integer in list, missing agency prefix, bare site number, and end-to-end get_daily checks
• Full test suite passes (128/128)

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