chore: golf proofs

[euprunin]

The goal of this golfing PR is to decrease the number of times lemmas are called explicitly (replacing calls to lemmas with calls to tactics). Any decrease in compilation time is a welcome side effect, although it is not a primary objective.

Trace profiling results (differences <20 ms considered measurement noise):

• DiscreteTiling.PlacedTile.ext_iff_of_exists: <20 ms before, 68 ms after
• ProbabilityTheory.Fernique.lintegral_exp_mul_sq_norm_le_mul: 1876 ms before, 1629 ms after 🎉

This golfing PR is batched under the following guidelines:

• Up to ~5 changed files per PR
• Up to ~25 changed declarations per PR
• Up to ~100 changed lines per PR

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[github-actions]

PR summary 946b120add

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

No declarations were harmed in the making of this PR! 🐙

You can run this locally as follows

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

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

The doc-module for scripts/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/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).