feat: add BEq to DHashMap/HashMap/HashSet and their extensional variants

[wkrozowski]

This PR adds BEq instance for DHashMap/HashMap/HashSet and their extensional variants and proves lemmas relating it to the equivalence of hashmaps/equality of extensional variants.

[leanprover-community-bot]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 75342961fcc7bbcc911ad0497d18d95b0f008de9 --onto 5a4226f2bdcc6299df76285b1d30f238546c09fe. You can force Mathlib CI using the force-mathlib-ci label. (2025-11-19 20:39:19)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 75342961fcc7bbcc911ad0497d18d95b0f008de9 --onto a106ea053fec080a50204b0ad6dadc69bc3f0937. You can force Mathlib CI using the force-mathlib-ci label. (2025-11-20 20:35:01)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 75342961fcc7bbcc911ad0497d18d95b0f008de9 --onto b0e6db322421ce368999f08870fd747e45242f86. You can force Mathlib CI using the force-mathlib-ci label. (2025-11-26 12:51:51)
• ❗ Mathlib CI can not be attempted yet, as the nightly-testing-2025-11-27 tag does not exist there yet. We will retry when you push more commits. If you rebase your branch onto nightly-with-mathlib, Mathlib CI should run now. You can force Mathlib CI using the force-mathlib-ci label. (2025-11-27 12:23:20)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 799d5944007085768dcc8b8558c6dae485d4ae22 --onto b0e6db322421ce368999f08870fd747e45242f86. You can force Mathlib CI using the force-mathlib-ci label. (2025-11-27 17:54:43)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 1ae680c5e2f3922ba0c6c257a105426fdab20999 --onto 5bd331e85d9d110a29fb3367dbb21854010ffcbd. You can force Mathlib CI using the force-mathlib-ci label. (2025-12-01 13:53:32)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 1ae680c5e2f3922ba0c6c257a105426fdab20999 --onto 0173444d24df9253d7947cfe82519e4a6caffd3a. You can force Mathlib CI using the force-mathlib-ci label. (2025-12-04 13:11:14)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 1ae680c5e2f3922ba0c6c257a105426fdab20999 --onto dd28f005889dd2fcca6fe0638133de561a655ad1. You can force Mathlib CI using the force-mathlib-ci label. (2025-12-04 18:08:38)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 1ae680c5e2f3922ba0c6c257a105426fdab20999 --onto 455fd0b4488e2adc85f825a52e2ee7d944a5740a. You can force Mathlib CI using the force-mathlib-ci label. (2025-12-05 14:43:36)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 1ae680c5e2f3922ba0c6c257a105426fdab20999 --onto 2ca3bc28590c5c33f755d3bd18252f25ea266266. You can force Mathlib CI using the force-mathlib-ci label. (2025-12-08 09:01:13)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 1ae680c5e2f3922ba0c6c257a105426fdab20999 --onto 62f2f9229356039356c0469a46d8ecd77be88e2a. You can force Mathlib CI using the force-mathlib-ci label. (2025-12-08 12:54:11)

[leanprover-bot]

Reference manual CI status:

• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase 75342961fcc7bbcc911ad0497d18d95b0f008de9 --onto d3dda9f6d4428a906c096067ecb75e432afc4615. You can force reference manual CI using the force-manual-ci label. (2025-11-19 20:39:20)
• ❗ Reference manual CI can not be attempted yet, as the nightly-testing-2025-11-27 tag does not exist there yet. We will retry when you push more commits. If you rebase your branch onto nightly-with-manual, reference manual CI should run now. You can force reference manual CI using the force-manual-ci label. (2025-11-27 12:23:22)
• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase 799d5944007085768dcc8b8558c6dae485d4ae22 --onto d3dda9f6d4428a906c096067ecb75e432afc4615. You can force reference manual CI using the force-manual-ci label. (2025-11-27 17:54:44)
• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase 1ae680c5e2f3922ba0c6c257a105426fdab20999 --onto d3dda9f6d4428a906c096067ecb75e432afc4615. You can force reference manual CI using the force-manual-ci label. (2025-12-01 13:53:34)

[wkrozowski]

Non-terminal simp