Remove ElementHolder backward-compatible tool aliases (PR #430 review)

[gupichon]

Description

Addresses kparasch's two review comments on #430 (Elementholder api refurbishment):

• ToolHolder's 7 default-tool properties (chromaticity, crm, tune, trm, orbit, orm, dispersion) went through self._peer.get_X_tuning(name), a parallel lookup path that does the exact same _TOOLS dict lookup as self.get(name), just with a slightly different error message. Simplified to use self.get(name) directly.
• ElementHolder kept 7 backward-compatible aliases (design.tune, .chromaticity, .orbit, .dispersion, .trm, .crm, .orm) for design.tool.<name>. Per review feedback, removed them outright rather than keep both spellings this early in development, and enforced design.tool.<name> as the only way to reach a mode's default tuning/measurement tool.

Related Issue

Review follow-up on #430 (part of epic #199, ElementHolder API refurbishment).
Not a separate tracked issue.

Features/issues described there are:

• bugfix/cleanup: removed redundant lookup indirection in ToolHolder and dropped duplicate top-level accessors on ElementHolder, per reviewer request, to keep a single way to reach each default tool.

Changes to existing functionality

• ElementHolder.tune/.chromaticity/.orbit/.dispersion/.trm/.crm/.orm properties removed. Every caller must now use design.tool.<name>. This is a breaking change for any code still using the short form.
• ToolHolder's 7 properties now call self.get(name) instead of self._peer.get_X_tuning(name). ElementHolder.get_X_tuning(name) (the named, non-default lookup methods) are unchanged and still part of the public API.

Testing

The following tests were updated (no new tests needed, this is a removal/simplification):

• ~44 call sites across tests/tuning_tools/test_tuning_dispersion.py, test_tuning_orm.py, test_tuning_orbit_correction.py, test_tuning_tools.py, and tests/diagnostics/test_diagnostic_accessors.py migrated to .tool.<name>
• tests/tuning_tools/test_tool_accessors.py migrated, and test_tool_typed_properties_alias_existing_defaults removed (it only asserted the now-gone alias equalled .tool.<name>, tautological once the alias is gone)
• examples/use_cases/01-tune_correction.{py,ipynb}, 03-orbit_correction.{py,ipynb}, examples/other_examples/ORM_Tango_server/ORM.py and the use_cases/README.md table updated to the new accessor

Verify that your checklist complies with the project

• New and existing unit tests pass locally
• Tests were added to prove that all features/changes are effective (existing coverage updated to exercise the new accessor path; no new behavior to cover)
• The code is commented where appropriate
• Any existing features are not broken (unless there is an explicit change to an existing functionality). The alias removal is exactly that explicit, reviewer-requested change

[gupichon]

@kparasch, could you take a look at this PR?

[kparasch]

ipynb files are my nightmare!

I think it looks good