Odoo now avoids repeated language checks during common cached reads, improving performance for translated content. It also validates languages when creating, updating, or fetching translated fields, reducing the risk of data being handled in the wrong fallback language.

[IMP] core: better lang check
Before this commit, we check if language is valid and active when `env.lang`.
1. SQL f'->>{env.lang}' is safe
2. `env.lang` is frequently called and slow

This commit
a) removes language check for `env.lang` to improve performance.
The field value reading time for translated field is reduced by 50% when the
field value has been cached.

b) adds language check when necessary
currently when you read/write in inactive or invalid language, you will actually
read/write in en_US. It would be safer to raise an error instead of doing
everything in en_US especially when some rpc read/write script forgets a
language is inactivated in the server

For feature, the added language validation happens when
1. `write` translated fields
2. `create` records with translated fields
3. `fetch` field values for translated fields

For performance the added language validation shouldn't happen when
1. `read` cached translated field value

c) for sake of a) the `env.lang` is not safe anymore
the following commits refactor SQL queries to avoid SQL injection with the help
of `_field_to_sql`

https://github.com/odoo/odoo/pull/142814

Planning settings now clearly separate shift swapping from employees unassigning themselves, making it easier for managers to choose the right behavior. Future-dated timesheets are also hidden from validation menus to avoid showing work items that cannot yet be approved.

Before this commit, it was not clear to users that the 'switch shifts'
feature existed, and that is it mutually exclusive with the 'allow unassignment'
option in the settings.

To make things clear, this commit splits the 'allowing unassignment'
setting in two:
- The 'switch shifts with other employees' option which corresponds to the
current behavior when the 'allow unassignment' feature is disabled. It is
the default value.
- The 'unassignment themselves from shifts' option which corresponds to
the current behavior when the 'allow unassignment' feature is enabled.

task-3703648

The GSTR return period form now hides the tax unit option when no tax unit is available. This keeps the form cleaner and avoids showing users an irrelevant choice.

In this PR
-------------

**[IMP] l10n_in_reports_gstr: hide tax unit if not available**
- This commits hides the tax unit for gstr return period form if no tax unit is available

task-3679488

Financial reports now include an option to display amounts in thousands, making large figures easier to read and compare. This helps users review high-level financial results more quickly without changing the underlying data.

Add an option/filter to display amount in thousands.

task-3626894

The online sales templates for rentals and subscriptions were simplified after related product page caching was removed. This keeps the website sales experience aligned with platform changes and should make future maintenance easier without changing visible business workflows.

Now that the cache has been removed from product page, those templates (or part of) can be simplified.

See also:
https://github.com/odoo/odoo/pull/145532
https://github.com/odoo/upgrade/pull/5422