feat(Analysis/InnerProductSpace): singleton basis for 1d space

[wwylele]

This was brought up in #36462. Similar to existing FiniteDimensional.basisSingleton, this provides a OrthonormalBasis version.

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[github-actions]

PR summary c0ee2a9375

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

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Declarations diff

+ FiniteDimensional.orthonormalBasisSingleton
+ FiniteDimensional.orthonormalBasisSingleton_apply
+ FiniteDimensional.toBasis_orthonormalBasisSingleton
+ Unique.orthonormal_iff

You can run this locally as follows

## summary with just the declaration names:
./scripts/pr_summary/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh contains some details about this script.

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No changes to technical debt.

You can run this locally as

./scripts/reporting/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).

[eric-wieser]

What do you think of changing this to

Suggested change

	theorem Unique.orthonormal_iff [Unique ι] {v : ι → E} : Orthonormal 𝕜 v ↔ ‖v default‖ = 1 := by
	theorem orthonormal_subsingleton_iff [Subsingleton ι] {v : ι → E} : Orthonormal 𝕜 v ↔ ∀ i, ‖v i‖ = 1 := by

which then applies to empty families too?