Allow user to change `rel_tolerance` in `to_grid_time` function

Explanation of changes

Long schedules can accumulate floating point errors beyond the tolerance that is specified inside the to_grid_time function. The threshold is now editable by the user:

import quantify_scheduler.backends.qblox.constants as constants

constants.GRID_TIME_TOLERANCE_TIME = 0.05

and a nicer error is produced by to_grid_time:

ValueError: Attempting to use a time value of 168345600000.003 ns. Please ensure that the durations of operations and wait times between operations are multiples of 4 ns (tolerance: 1e-03 ns). If you think this is a mistake, try increasing the tolerance by setting e.g. `quantify_scheduler.backends.qblox.constants.GRID_TIME_TOLERANCE_TIME = 1e-2` at the top of your script.

See also !1102 (merged) .

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Merge checklist

See also merge request guidelines

• Merge request has been reviewed (in-depth by a knowledgeable contributor), and is approved by a project maintainer.
• New code is covered by unit tests (or N/A).
• New code is documented and docstrings use numpydoc format (or N/A).
• New functionality: considered making private instead of extending public API (or N/A).
• Public API changed: added @deprecated and entry in deprecated code suggestions (or N/A).
• Newly added/adjusted documentation and docstrings render properly (or N/A).
• Pipeline fix or dependency update: post in #software-for-developers channel to merge main back in or update local packages (or N/A).
• Tested on hardware (or N/A).
• CHANGELOG.md for breaking changes and AUTHORS.md have been updated (or N/A).
• Update Hardware backends documentation if backend interface change or N/A
• Check whether performance is significantly affected by looking at the Performance metrics results.
• Windows tests in CI pipeline pass (manually triggered by maintainers before merging).
  • Maintainers do not hit Auto-merge, we need to actively check as manual tests do not block pipeline

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