Bloq namespacing and display (__str__) updates.

[mpharrigan]

As part of #1824 , I want to be better about our convention for importing bloqs and __str__ representations in the qualtran standard library (i.e. qualtran.bloqs). There's no additional restriction on custom, user-authored bloqs. These changes make sure:

• bloqs are generally imported "one level up" from their file. e.g. ControlledAddOrSubtract is defined in qualtran/bloqs/arithmetic/controlled_add_or_subtract.py but it prefers to be imported from qualtran.bloqs.arithmetic. This is codified in the (existing) default _pkg_(cls) -> str classmethod. You can override it if you want something different.
• The __str__ representation looks like an object string (cc Qualtran-L1: Objectstrings #1823). This PR removes some special symbols in favor of more Python-looking strings.

note that this causes more bloq examples to be loadable (visible in the re-generated manifest)

[gemini-code-assist]

Code Review

This pull request is a nice improvement for the library, enhancing bloq namespacing and making __str__ representations more consistent and Python-like. The changes are well-structured and include relevant tests. I have two suggestions for improvement. First, to maintain consistency across the basic rotation gates, I recommend adding a CRx bloq and a specialized get_ctrl_system for Rx, similar to what has been done for Ry in this PR. Second, the new wire_symbol implementation in the Power bloq could be made more robust to handle different types of wire symbols for bloq titles. I've provided a code suggestion for a cleaner and more resilient implementation.

[gemini-code-assist]

This is a great addition! For consistency with Ry and Rz, it would be good to also add a specialized get_ctrl_system for Rx. This would involve creating a CRx bloq, similar to how CRy was added in this PR. The _controlled_rp_circuit helper is already generic enough to support this.

You could add the following CRx class:

@frozen
class CRx(Bloq):
    r"""A controlled Rx rotation."""
    angle: SymbolicFloat
    eps: SymbolicFloat = 1e-11

    @cached_property
    def signature(self) -> 'Signature':
        return Signature.build(ctrl=1, q=1)

    def build_composite_bloq(
        self, bb: 'BloqBuilder', ctrl: 'Soquet', q: 'Soquet'
    ) -> Dict[str, 'SoquetT']:
        return _controlled_rp_circuit(
            bb, single_q_pow_cls=XPowGate, angle=self.angle, eps=self.eps, ctrl=ctrl, q=q
        )

    def __str__(self):
        return f'CRx({self.angle})'

And then add this method to the Rx class:

    def get_ctrl_system(self, ctrl_spec: 'CtrlSpec') -> Tuple['Bloq', 'AddControlledT']:
        if ctrl_spec != CtrlSpec():
            return super().get_ctrl_system(ctrl_spec)

        from qualtran.bloqs.mcmt.specialized_ctrl import get_ctrl_system_1bit_cv_from_bloqs

        return get_ctrl_system_1bit_cv_from_bloqs(
            bloq=self,
            ctrl_spec=ctrl_spec,
            current_ctrl_bit=None,
            bloq_with_ctrl=CRx(self.angle, eps=self.eps),
            ctrl_reg_name='ctrl',
        )